diff --git a/src/aare/common/find_xtal.py b/src/aare/common/find_xtal.py
index 23468175..6433fa10 100644
--- a/src/aare/common/find_xtal.py
+++ b/src/aare/common/find_xtal.py
@@ -314,4 +314,300 @@ def has_sufficient_low_res_spots(
         )
         return False
 
-    return True
\ No newline at end of file
+    return True
+
+
+def compute_crystal_score_array(
+    scan_results: List,
+    w_bkg: float = 0.25,
+    w_low_res: float = 0.55,
+    w_indexed: float = 0.20,
+) -> np.ndarray:
+    """Combine bkg (25%), spots_low_res (55%), and spots_indexed (20%) into a 0–100 score.
+
+    Each field is min-max normalised to [0, 100] within the grid before weighting,
+    so the final score is the probability (0–100) that a pixel belongs to a crystal.
+    """
+    arr_bkg = rebuild_array_from_scan_results(scan_results, "bkg")
+    arr_low = rebuild_array_from_scan_results(scan_results, "spots_low_res")
+    arr_idx = rebuild_array_from_scan_results(scan_results, "spots_indexed")
+
+    def _norm(a: np.ndarray) -> np.ndarray:
+        mn, mx = float(a.min()), float(a.max())
+        if mx == mn:
+            return np.zeros_like(a, dtype=float)
+        return (a - mn) / (mx - mn) * 100.0
+
+    return w_bkg * _norm(arr_bkg) + w_low_res * _norm(arr_low) + w_indexed * _norm(arr_idx)
+
+
+def _max_cell(arr: np.ndarray) -> tuple[int, int]:
+    """Return (nx, ny) of the cell with the highest value."""
+    idx = np.unravel_index(np.argmax(arr), arr.shape)
+    return int(idx[0]), int(idx[1])
+
+
+def _draw_panel(
+    ax,
+    arr: np.ndarray,
+    mask: np.ndarray,
+    label: str,
+    threshold: float,
+    grid_size_mm: Optional[tuple[float, float]] = None,
+    cbar_label: str = "spots_low_res",
+) -> None:
+    """Shared helper: heatmap + crystal contour + max-cell square on one Axes.
+
+    If grid_size_mm=(step_x_mm, step_y_mm) is provided, the crystal size in µm
+    is computed via get_xtal_size and shown in the panel title.
+    """
+    import matplotlib.patches as mpatches
+    import matplotlib.pyplot as plt
+    from aare.common.coordinate import Coordinate
+
+    n_nx, n_ny = arr.shape
+    max_nx, max_ny = _max_cell(arr)
+    n_cells = int(mask.sum())
+
+    im = ax.imshow(
+        arr.T,
+        origin="lower",
+        cmap="viridis",
+        aspect="equal",
+        extent=[-0.5, n_nx - 0.5, -0.5, n_ny - 0.5],
+    )
+    plt.colorbar(im, ax=ax, label=cbar_label, fraction=0.046, pad=0.04)
+    ax.contour(
+        np.arange(n_nx), np.arange(n_ny), mask.T.astype(float),
+        levels=[0.5],
+        colors="cyan",
+        linewidths=1.8,
+    )
+    rect = mpatches.Rectangle(
+        (max_nx - 0.5, max_ny - 0.5), 1, 1,
+        linewidth=2, edgecolor="red", facecolor="none",
+    )
+    ax.add_patch(rect)
+
+    size_line = ""
+    if grid_size_mm is not None and n_cells > 0:
+        r = RasterGridRequest(
+            exp_time_s=0.0,
+            n_x=n_nx,
+            n_y=n_ny,
+            grid_size_mm=Coordinate(x=grid_size_mm[0], y=grid_size_mm[1]),
+            smargon_top_left=None,
+        )
+        xtal_size = get_xtal_size(CrystalSize(x=0, y=0, z=0), mask.astype(float), r)
+        size_line = f"\n{xtal_size.x:.0f}×{xtal_size.y:.0f} µm"
+
+    ax.set_title(
+        f"{label}\nthresh≈{threshold:.1f}  |  {n_cells} cells{size_line}",
+        fontsize=8,
+    )
+    ax.set_xlabel("nx", fontsize=7)
+    ax.set_ylabel("ny", fontsize=7)
+    ax.tick_params(labelsize=6)
+
+
+# ── Clustering / thresholding methods ─────────────────────────────────────────
+
+def crystal_mask_corner_background(arr: np.ndarray) -> tuple[np.ndarray, float]:
+    """Threshold = max(far-corner value, floor=10).
+
+    Simple, parameter-free.  Returns too many cells when corners are zero
+    because any nonzero value passes.
+    """
+    n_nx, n_ny = arr.shape
+    corners = [arr[0, 0], arr[n_nx - 1, 0], arr[0, n_ny - 1], arr[n_nx - 1, n_ny - 1]]
+    threshold = max(float(np.max(corners)), 10.0)
+    return arr > threshold, threshold
+
+
+def crystal_mask_otsu_nonzero(arr: np.ndarray) -> tuple[np.ndarray, float]:
+    """Otsu threshold computed only on the nonzero values.
+
+    Finds the natural gap in the signal distribution.
+    Ignores the large mass of background zeros so the threshold is
+    placed within the diffraction-signal population.
+    """
+    from skimage.filters import threshold_otsu
+
+    nonzero = arr[arr > 0]
+    if nonzero.size == 0:
+        return np.zeros_like(arr, dtype=bool), 0.0
+    threshold = float(threshold_otsu(nonzero))
+    return arr > threshold, threshold
+
+
+def crystal_mask_mean_sigma(arr: np.ndarray, n_sigma: float = 0.5) -> tuple[np.ndarray, float]:
+    """Threshold = mean + n_sigma * std of nonzero values.
+
+    n_sigma=0.5 keeps cells within ~1/2 std above average signal.
+    Raise n_sigma to tighten the region around the strongest-diffracting core.
+    """
+    nonzero = arr[arr > 0]
+    if nonzero.size == 0:
+        return np.zeros_like(arr, dtype=bool), 0.0
+    threshold = float(nonzero.mean() + n_sigma * nonzero.std())
+    return arr > threshold, threshold
+
+
+def crystal_mask_signal_percentile(arr: np.ndarray, percentile: float = 60.0) -> tuple[np.ndarray, float]:
+    """Threshold = given percentile of nonzero values.
+
+    percentile=60 keeps the top 40 % of signal cells; raise to sharpen.
+    Unlike mean+sigma this is robust to heavy-tailed distributions.
+    """
+    nonzero = arr[arr > 0]
+    if nonzero.size == 0:
+        return np.zeros_like(arr, dtype=bool), 0.0
+    threshold = float(np.percentile(nonzero, percentile))
+    return arr > threshold, threshold
+
+
+def crystal_mask_dbscan(arr: np.ndarray, min_signal: float = 10.0,
+                        eps: float = 1.5, min_samples: int = 3) -> tuple[np.ndarray, float]:
+    """DBSCAN spatial clustering on cells with signal > min_signal.
+
+    Groups adjacent diffracting cells into clusters; the largest cluster
+    (by total signal weight) is labelled as the crystal.
+    eps=1.5 connects cells that are one grid step apart (including diagonal).
+    """
+    from sklearn.cluster import DBSCAN
+
+    ys, xs = np.where(arr > min_signal)
+    if len(ys) == 0:
+        return np.zeros_like(arr, dtype=bool), min_signal
+
+    coords = np.column_stack([ys, xs]).astype(float)
+    labels = DBSCAN(eps=eps, min_samples=min_samples).fit_predict(coords)
+
+    best_label, best_weight = -1, -1.0
+    for lbl in set(labels):
+        if lbl == -1:
+            continue
+        weight = float(arr[ys[labels == lbl], xs[labels == lbl]].sum())
+        if weight > best_weight:
+            best_label, best_weight = lbl, weight
+
+    mask = np.zeros_like(arr, dtype=bool)
+    if best_label != -1:
+        sel = labels == best_label
+        mask[ys[sel], xs[sel]] = True
+    return mask, min_signal
+
+
+def crystal_mask_kmeans(arr: np.ndarray, n_clusters: int = 3) -> tuple[np.ndarray, float]:
+    """K-means on signal values (1-D feature).
+
+    Splits cells into n_clusters groups; the cluster with the highest
+    centroid is the crystal.  n_clusters=3 separates background / fringe / crystal.
+    """
+    from sklearn.cluster import KMeans
+
+    flat = arr.flatten().reshape(-1, 1)
+    km = KMeans(n_clusters=n_clusters, random_state=0, n_init="auto").fit(flat)
+    crystal_label = int(np.argmax(km.cluster_centers_.flatten()))
+    threshold = float(sorted(km.cluster_centers_.flatten())[-2])
+    mask = (km.labels_.reshape(arr.shape) == crystal_label)
+    return mask, threshold
+
+
+CRYSTAL_METHOD_MAP: dict = {
+    "corner": ("Corner background", crystal_mask_corner_background),
+    "otsu": ("Otsu (nonzero)", crystal_mask_otsu_nonzero),
+    "mean_sigma": ("Mean + 0.5σ", lambda arr: crystal_mask_mean_sigma(arr, n_sigma=0.5)),
+    "percentile": ("Top-40% signal", lambda arr: crystal_mask_signal_percentile(arr, percentile=60.0)),
+    "dbscan": ("DBSCAN (spatial)", crystal_mask_dbscan),
+    "kmeans": ("K-means (k=3)", crystal_mask_kmeans),
+}
+
+
+def compare_crystal_methods(
+    results: List,
+    arr: Optional[np.ndarray] = None,
+    grid_size_mm: Optional[tuple[float, float]] = None,
+) -> None:
+    """Plot each crystal-detection method side-by-side for visual comparison.
+
+    Cyan contour = detected crystal region.
+    Red square   = cell with maximum spots_low_res.
+    grid_size_mm = (step_x_mm, step_y_mm) — when provided, crystal size in µm
+                   is calculated via get_xtal_size and shown in each panel title.
+    """
+    import matplotlib.pyplot as plt
+
+    if arr is None:
+        arr = rebuild_array_from_scan_results(results, "spots_low_res")
+
+    methods = [
+        ("Corner background", *crystal_mask_corner_background(arr)),
+        ("Otsu (nonzero)", *crystal_mask_otsu_nonzero(arr)),
+        ("Mean + 0.5σ", *crystal_mask_mean_sigma(arr, n_sigma=0.5)),
+        ("Top-40% signal", *crystal_mask_signal_percentile(arr, percentile=60.0)),
+        ("DBSCAN (spatial)", *crystal_mask_dbscan(arr)),
+        ("K-means (k=3)", *crystal_mask_kmeans(arr)),
+    ]
+
+    fig, axes = plt.subplots(2, 3, figsize=(14, 9))
+    for ax, (label, mask, threshold) in zip(axes.flat, methods):
+        _draw_panel(ax, arr, mask, label, threshold, grid_size_mm=grid_size_mm)
+
+    fig.suptitle("Crystal region detection — method comparison\n"
+                 "cyan = crystal outline  |  red square = max spots_low_res cell",
+                 fontsize=10)
+    plt.tight_layout()
+    plt.show()
+
+
+def compare_crystal_methods_scored(
+    results: List,
+    score_arr: Optional[np.ndarray] = None,
+    method: Optional[str] = None,
+    grid_size_mm: Optional[tuple[float, float]] = None,
+    w_bkg: float = 0.20,
+    w_low_res: float = 0.60,
+    w_indexed: float = 0.20,
+) -> None:
+    """Plot each crystal-detection method applied to the composite 0–100 crystal score.
+
+    The score combines bkg (w_bkg), spots_low_res (w_low_res), and spots_indexed
+    (w_indexed), each min-max normalised.  All six methods are shown side-by-side.
+
+    Args:
+        results:      scan result list (used to build score if score_arr is None)
+        score_arr:    pre-computed score array; computed from results when None
+        method:       if given (one of 'corner','otsu','mean_sigma','percentile',
+                      'dbscan','kmeans'), that panel is highlighted with a yellow border
+        grid_size_mm: (step_x_mm, step_y_mm) for crystal-size annotation
+        w_bkg, w_low_res, w_indexed: composite score weights (must sum to 1.0)
+    """
+    import matplotlib.pyplot as plt
+
+    if score_arr is None:
+        score_arr = compute_crystal_score_array(results, w_bkg=w_bkg, w_low_res=w_low_res, w_indexed=w_indexed)
+
+    method_entries = [
+        (name, label, fn)
+        for name, (label, fn) in CRYSTAL_METHOD_MAP.items()
+    ]
+
+    fig, axes = plt.subplots(2, 3, figsize=(15, 9))
+    for ax, (name, label, fn) in zip(axes.flat, method_entries):
+        mask, threshold = fn(score_arr)
+        _draw_panel(ax, score_arr, mask, label, threshold,
+                    grid_size_mm=grid_size_mm, cbar_label="crystal score (0–100)")
+        if method and name == method:
+            for spine in ax.spines.values():
+                spine.set_edgecolor("yellow")
+                spine.set_linewidth(3)
+
+    weight_note = f"bkg×{w_bkg:.0%}  +  spots_low_res×{w_low_res:.0%}  +  spots_indexed×{w_indexed:.0%}"
+    fig.suptitle(
+        f"Crystal region detection on composite score  [{weight_note}]\n"
+        "cyan = crystal outline  |  red square = max-score cell  |  score range 0–100",
+        fontsize=10,
+    )
+    plt.tight_layout()
+    plt.show()
\ No newline at end of file
diff --git a/src/aare/common/raster_grid.py b/src/aare/common/raster_grid.py
index 7c4327ff..676cf2d9 100644
--- a/src/aare/common/raster_grid.py
+++ b/src/aare/common/raster_grid.py
@@ -32,6 +32,10 @@ class RasterGridRequest(BaseModel):
 
     visible: bool = True
 
+    # When True, skip all hardware and generate simulated diffraction data.
+    # The file_prefix will have "_SIMU" appended so the DB record is identifiable.
+    no_beam: bool = False
+
     def get_image_number(self) -> int:
         return self.n_x * self.n_y
 
diff --git a/src/aare/common/simulate_raster.py b/src/aare/common/simulate_raster.py
new file mode 100644
index 00000000..5cc51e20
--- /dev/null
+++ b/src/aare/common/simulate_raster.py
@@ -0,0 +1,214 @@
+"""
+Synthetic raster scan data for no-beam / offline testing.
+
+Entry point
+-----------
+generate_no_beam_scan_result(request, seed=None) -> ScanResult
+
+The returned ScanResult is structurally identical to a real one, so all
+find_xtal.py functions consume it without modification.
+
+Pre-defined seeds
+-----------------
+Each seed fixes cluster geometry so results are reproducible.  The six
+scenarios below cover the main cases needed for unit-testing crystal-finding
+algorithms.
+
+Seed  Scenario
+----  --------
+1     Single crystal, centred – baseline positive detection
+2     Single crystal, off-centre – tests COM accuracy near an edge
+3     Two well-separated crystals – multi-crystal detection
+4     Two overlapping crystals – segmentation challenge
+5     Two clusters at ~90 ° – twinned / differently oriented crystal
+6     Pure background only – true negative (no crystal)
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import List
+
+import numpy as np
+from jfjoch_client import ScanResult
+from jfjoch_client.models.scan_result_images_inner import ScanResultImagesInner
+
+from aare.common.raster_grid import RasterGridRequest
+
+# ---------------------------------------------------------------------------
+# Cluster geometry descriptor
+# ---------------------------------------------------------------------------
+
+@dataclass
+class _ClusterParams:
+    """Fractional coordinates and shape of one elliptical crystal cluster.
+
+    cx, cy   – cluster centre as a fraction of (n_x, n_y)  [0..1]
+    ax, ay   – semi-axes as a fraction of (n_x, n_y)
+    theta    – rotation of the ellipse in radians
+    peak     – peak spots_low_res at cluster centre (integer)
+    """
+    cx: float
+    cy: float
+    ax: float
+    ay: float
+    theta: float
+    peak: int
+
+
+@dataclass
+class _SeedConfig:
+    clusters: List[_ClusterParams] = field(default_factory=list)
+
+
+# ---------------------------------------------------------------------------
+# Pre-defined seed catalogue
+# ---------------------------------------------------------------------------
+
+SEED_CATALOGUE: dict[int, _SeedConfig] = {
+    # --- 1: single crystal, centred, compact, strong signal ----------------
+    1: _SeedConfig(clusters=[
+        _ClusterParams(cx=0.50, cy=0.50, ax=0.15, ay=0.15, theta=0.0,  peak=120),
+    ]),
+
+    # --- 2: single crystal, off-centre, slightly elongated -----------------
+    2: _SeedConfig(clusters=[
+        _ClusterParams(cx=0.25, cy=0.70, ax=0.12, ay=0.18, theta=0.35, peak=90),
+    ]),
+
+    # --- 3: two well-separated crystals ------------------------------------
+    3: _SeedConfig(clusters=[
+        _ClusterParams(cx=0.20, cy=0.20, ax=0.12, ay=0.12, theta=0.0,  peak=100),
+        _ClusterParams(cx=0.75, cy=0.72, ax=0.15, ay=0.10, theta=0.2,  peak=80),
+    ]),
+
+    # --- 4: two overlapping crystals (centres ~1 sigma apart) --------------
+    4: _SeedConfig(clusters=[
+        _ClusterParams(cx=0.40, cy=0.45, ax=0.18, ay=0.15, theta=0.0,  peak=110),
+        _ClusterParams(cx=0.58, cy=0.55, ax=0.16, ay=0.18, theta=0.5,  peak=95),
+    ]),
+
+    # --- 5: two clusters with ~90° different orientations (twinned) --------
+    5: _SeedConfig(clusters=[
+        _ClusterParams(cx=0.30, cy=0.40, ax=0.25, ay=0.08, theta=0.0,  peak=105),
+        _ClusterParams(cx=0.68, cy=0.62, ax=0.08, ay=0.25, theta=0.0,  peak=100),
+    ]),
+
+    # --- 6: pure background, no crystal – true negative --------------------
+    6: _SeedConfig(clusters=[]),
+}
+
+
+# ---------------------------------------------------------------------------
+# Core generation
+# ---------------------------------------------------------------------------
+
+def _gaussian_cluster(
+    ix: np.ndarray,
+    iy: np.ndarray,
+    p: _ClusterParams,
+    n_x: int,
+    n_y: int,
+) -> np.ndarray:
+    """Return a 2-D Gaussian signal array for one cluster.
+
+    ix, iy are integer coordinate grids with shape (n_x, n_y).
+    """
+    cx = p.cx * (n_x - 1)
+    cy = p.cy * (n_y - 1)
+
+    dx = (ix - cx) / max(p.ax * n_x, 0.5)
+    dy = (iy - cy) / max(p.ay * n_y, 0.5)
+
+    cos_t = np.cos(p.theta)
+    sin_t = np.sin(p.theta)
+    dx_r =  dx * cos_t + dy * sin_t
+    dy_r = -dx * sin_t + dy * cos_t
+
+    return p.peak * np.exp(-2.0 * (dx_r ** 2 + dy_r ** 2))
+
+
+def generate_no_beam_scan_result(
+    request: RasterGridRequest,
+    seed: int | None = None,
+) -> ScanResult:
+    """Build a synthetic ScanResult for no-beam / offline operation.
+
+    Parameters
+    ----------
+    request:
+        The grid request whose n_x, n_y, and file_prefix are used.
+    seed:
+        Integer 1-6 selects a pre-defined scenario from SEED_CATALOGUE.
+        Any other value (or None) draws cluster parameters randomly using
+        the seed as an RNG seed (None → fully random).
+
+    Returns
+    -------
+    ScanResult
+        Populated with one ScanResultImagesInner per grid cell, with
+        realistic background noise and optional crystal cluster(s).
+    """
+    n_x = max(request.n_x, 1)
+    n_y = max(request.n_y, 1)
+
+    rng = np.random.default_rng(seed)
+
+    # Coordinate grids
+    ix, iy = np.meshgrid(np.arange(n_x), np.arange(n_y), indexing="ij")
+
+    # Background: Poisson noise, mean ≈ 3 counts
+    bkg = rng.poisson(lam=3.0, size=(n_x, n_y)).astype(float)
+
+    # Crystal signal layer (spots_low_res)
+    signal = np.zeros((n_x, n_y), dtype=float)
+
+    if seed in SEED_CATALOGUE:
+        cfg = SEED_CATALOGUE[seed]
+        clusters = cfg.clusters
+    else:
+        # Random fallback: 1 or 2 clusters
+        n_clusters = rng.integers(1, 3)
+        clusters = [
+            _ClusterParams(
+                cx=rng.uniform(0.15, 0.85),
+                cy=rng.uniform(0.15, 0.85),
+                ax=rng.uniform(0.12, 0.30),
+                ay=rng.uniform(0.12, 0.30),
+                theta=rng.uniform(0, np.pi),
+                peak=int(rng.integers(50, 150)),
+            )
+            for _ in range(n_clusters)
+        ]
+
+    for p in clusters:
+        signal += _gaussian_cluster(ix, iy, p, n_x, n_y)
+
+    # Add Poisson noise on top of the crystal signal
+    spots_low_res = rng.poisson(lam=np.maximum(signal, 0)).astype(int)
+
+    # Assemble image list – one entry per grid cell in row-major order
+    images: list[ScanResultImagesInner] = []
+    for xi in range(n_x):
+        for yi in range(n_y):
+            img_number = xi * n_y + yi
+            images.append(ScanResultImagesInner(
+                number=img_number,
+                nx=xi,
+                ny=yi,
+                efficiency=1.0,
+                bkg=float(bkg[xi, yi]),
+                spots=int(spots_low_res[xi, yi]),
+                spots_low_res=int(spots_low_res[xi, yi]),
+                spots_indexed=0,
+                spots_ice=0,
+                index=0,
+                b=0.0,
+                res=None,
+                pixel_sum=None,
+                max=None,
+                sat=None,
+                err=None,
+            ))
+
+    return ScanResult(file_prefix=request.file_prefix, images=images)
diff --git a/src/aare/daq/daq.py b/src/aare/daq/daq.py
index 14bd5164..8e1c9210 100644
--- a/src/aare/daq/daq.py
+++ b/src/aare/daq/daq.py
@@ -33,6 +33,7 @@ from aare.common.models import (
     SimpleScanParameters, MLBoxModel, FluorescenceSpectrumParameterModel,
     FluorescenceSpectrumOutputModel)
 from aare.common.raster_grid import RasterGridRequest, CompletedRasterGrid, CompletedRasterGridElem
+from aare.common.simulate_raster import generate_no_beam_scan_result
 from aare.common.rotation_scan import RotationScanRequest, CompletedRotationScan
 from aare.common.sample_geometry import SampleGeometryModel
 from aare.daq.spreadsheetupdater import beamline
@@ -917,6 +918,30 @@ class AareDAQ:
             if self.sample is not None and self.sample.db_id is not None:
                 self.__aare.create_gridscan_run(self.sample, request, status)
 
+            if request.no_beam:
+                request = copy.deepcopy(request)
+                if request.file_prefix:
+                    request.file_prefix = f"{request.file_prefix}_SIMU"
+                logger.info("No beam mode: skipping hardware, generating simulated raster result.")
+                scan_result = generate_no_beam_scan_result(request)
+                sample_id = self.sample.db_id if self.sample and self.sample.db_id is not None else None
+                if sample_id:
+                    self.__set_state(BeamlineStateEnum.SampleAlignment)
+                    self.save_screenshot_db(sample_id, f"{sample_id}_post_raster_{request.omega_deg}deg")
+                    self.__aare.ingest_gridscan(
+                        sample=self.sample,
+                        raster_result=scan_result,
+                        raster_request=request,
+                        geom=self.sample_geometry,
+                        com=None,
+                        beam_mark_pxl=self.__cfg.get_beam_mark(self.zoom),
+                    )
+                return CompletedRasterGridElem(
+                    request=request,
+                    result=scan_result,
+                    centre_of_mass=None,
+                )
+
             if not self.__cfg.simulated_detector:
                 logger.info("initialise detector")
                 self.__jfjoch.measure_raster(request, status)