diff --git a/ophyd/sim.py b/ophyd/sim.py
index 632fbecc4..a0d6971a6 100644
--- a/ophyd/sim.py
+++ b/ophyd/sim.py
@@ -14,6 +14,7 @@
 from types import SimpleNamespace
 
 import numpy as np
+import scipy
 
 from .areadetector.base import EpicsSignalWithRBV
 from .areadetector.paths import EpicsPathSignal
@@ -648,6 +649,108 @@ def exposure_time(self, v):
         self.val.exposure_time = v
 
 
+
+class SynFunc(Device):
+    """
+    Evaluate a point on an arbitrary function based on the value of a motor.
+
+    Parameters
+    ----------
+    name : string
+    motor : Device
+    motor_field : string
+    response_function : function from R -> R
+    noise : {'poisson', 'uniform', None}, optional
+        Add noise to the function peak.
+    noise_multiplier : float, optional
+        Only relevant for 'uniform' noise. Multiply the random amount of
+        noise by 'noise_multiplier'
+    random_state : numpy random state object, optional
+        np.random.RandomState(0), to generate random number with given seed
+
+    Example
+    -------
+    motor = SynAxis(name='motor')
+    response_function = -scipy.special.erf
+    det = SynFunc('det', motor, 'motor', response_function)
+    """
+
+    def _compute(self):
+        m = self._motor.read()[self._motor_field]["value"]
+        # we need to do this one at a time because
+        #   - self.read() may be screwed with by the user
+        #   - self.get() would cause infinite recursion
+        noise = self.noise.get()
+        noise_multiplier = self.noise_multiplier.get()
+        v = self._response_function(m)
+        if noise == "poisson":
+            v = int(self.random_state.poisson(np.round(v), 1))
+        elif noise == "uniform":
+            v += self.random_state.uniform(-1, 1) * noise_multiplier
+        return v
+
+    val = Cpt(SynSignal, kind="hinted")
+    noise = Cpt(
+        EnumSignal,
+        value="none",
+        kind="config",
+        enum_strings=("none", "poisson", "uniform"),
+    )
+    noise_multiplier = Cpt(Signal, value=1, kind="config")
+
+    def __init__(
+        self, name, motor, motor_field, response_function, *, random_state=None, **kwargs
+    ):
+        set_later = {}
+        for k in ("noise", "noise_multiplier"):
+            v = kwargs.pop(k, None)
+            if v is not None:
+                set_later[k] = v
+        super().__init__(name=name, **kwargs)
+        self._motor = motor
+        self._motor_field = motor_field
+        self._response_function = response_function
+
+        self.random_state = random_state or np.random
+        self.val.name = self.name
+        self.val.sim_set_func(self._compute)
+        for k, v in set_later.items():
+            getattr(self, k).put(v)
+
+        self.trigger()
+
+    def subscribe(self, *args, **kwargs):
+        return self.val.subscribe(*args, **kwargs)
+
+    def clear_sub(self, cb, event_type=None):
+        return self.val.clear_sub(cb, event_type=event_type)
+
+    def unsubscribe(self, cid):
+        return self.val.unsubscribe(cid)
+
+    def unsubscribe_all(self):
+        return self.val.unsubscribe_all()
+
+    def trigger(self, *args, **kwargs):
+        return self.val.trigger(*args, **kwargs)
+
+    @property
+    def precision(self):
+        return self.val.precision
+
+    @precision.setter
+    def precision(self, v):
+        self.val.precision = v
+
+    @property
+    def exposure_time(self):
+        return self.val.exposure_time
+
+    @exposure_time.setter
+    def exposure_time(self, v):
+        self.val.exposure_time = v
+
+
 class Syn2DGauss(Device):
     """
     Evaluate a point on a Gaussian based on the value of a motor.
@@ -1551,6 +1654,17 @@ def hw(save_path=None):
         noise_multiplier=0.1,
         labels={"detectors"},
     )
+    def det_func(x):
+        return -scipy.special.erf(x) + 1.1
+    noisy_func_det = SynFunc(
+        "noisy_func_det",
+        motor,
+        "motor",
+        det_func,
+        noise="uniform",
+        noise_multiplier=0.1,
+        labels={"detectors"},
+    )
     det = SynGauss(
         "det", motor, "motor", center=0, Imax=1, sigma=1, labels={"detectors"}
     )
@@ -1642,6 +1756,7 @@ def hw(save_path=None):
         jittery_motor1=jittery_motor1,
         jittery_motor2=jittery_motor2,
         noisy_det=noisy_det,
+        noisy_func_det=noisy_func_det,
         det=det,
         identical_det=identical_det,
         det1=det1,