diff --git a/uc2rest/UC2Client.py b/uc2rest/UC2Client.py
index 6856926..e874526 100644
--- a/uc2rest/UC2Client.py
+++ b/uc2rest/UC2Client.py
@@ -22,6 +22,7 @@
 from .modules import Modules
 from .digitalout import DigitalOut
 from .digitalin import DigitalIn
+from .gpio import GPIO
 from .rotator import Rotator
 from .logger import Logger
 from .cmdrecorder import cmdRecorder
@@ -155,7 +156,10 @@ def __init__(self, host=None, port=31950, serialport=None, identity="UC2_Feather
         
         # initialize digital in
         self.digitalin = DigitalIn(self)
-        
+
+        # initialize GPIO / collision-detector slave interface
+        self.gpio = GPIO(self)
+
         # initialize messaging
         self.message = Message(self)
         
diff --git a/uc2rest/gpio.py b/uc2rest/gpio.py
new file mode 100644
index 0000000..864f721
--- /dev/null
+++ b/uc2rest/gpio.py
@@ -0,0 +1,155 @@
+"""GPIO / collision-detector interface for the UC2 CAN GPIO slave.
+
+The CAN master exposes the GPIO slave (XIAO node, default CAN node-id 60)
+through two serial endpoints:
+
+    {"task":"/gpio_get"}
+        -> {"gpio":{"node":60,"mean":585,"filtered":584,"raw":581,
+                    "reference":585,"threshold":150,"sensitivity":4,
+                    "trip":0,"estop":0},"ok":true,"qid":N}
+
+    {"task":"/gpio_act","threshold":150,"sensitivity":4,
+     "reference":585,"calibrate":1}          (all value fields optional)
+
+Collision detection runs ON THE SLAVE: the sensor has an idle value (the
+"reference"); a collision = `sensitivity` consecutive samples deviating more
+than `threshold` ADC counts from the reference (rising OR falling). Sensor
+values are never streamed on the CAN bus — polling /gpio_get triggers SDO
+reads on demand. Only the collision/E-stop EVENT is pushed asynchronously;
+the master then prints:
+
+    {"gpio":{"event":1,"node":60,"trip":1,"estop":0,"flags":3,
+             "filtered":2365,"raw":2937,...}}
+
+The "event":1 marker distinguishes pushed edges from /gpio_get responses
+(both share the top-level "gpio" key and therefore both arrive at the same
+serial callback).
+"""
+
+
+class GPIO(object):
+    def __init__(self, parent):
+        self._parent = parent
+
+        # last known state (merged from get_status responses and async events)
+        self.status = {}
+
+        # register a callback for any {"gpio":{...}} frame on the serial loop
+        if hasattr(self._parent, "serial"):
+            self._parent.serial.register_callback(self._callback_gpio, pattern="gpio")
+
+        # user-registered callbacks
+        self._collision_callbacks = []   # fired on async trip/clear events
+        self._status_callbacks = []      # fired on every gpio frame
+
+    # ─────────────────────────────────────────────────────────────────
+    # Async event plumbing
+    # ─────────────────────────────────────────────────────────────────
+    def _callback_gpio(self, data):
+        """Handle any serial frame with a top-level "gpio" key.
+
+        Pushed events carry "event":1 and fire the collision callbacks;
+        /gpio_get responses only refresh the cached status."""
+        try:
+            gpio = data.get("gpio", None)
+            if not isinstance(gpio, dict):
+                return
+            self.status.update(gpio)
+
+            for cb in self._status_callbacks:
+                try:
+                    cb(dict(self.status))
+                except Exception as e:
+                    print(f"Error in gpio status callback: {e}")
+
+            if gpio.get("event", 0):
+                for cb in self._collision_callbacks:
+                    try:
+                        cb(dict(gpio))
+                    except Exception as e:
+                        print(f"Error in gpio collision callback: {e}")
+        except Exception as e:
+            print("Error in _callback_gpio: ", e)
+
+    def register_collision_callback(self, callbackfct):
+        """Register a function called on every asynchronously pushed GPIO
+        event (collision trip/clear, E-stop press/release). The callback
+        receives the event dict, e.g. {"event":1,"trip":1,"estop":0,...}.
+        Check ["trip"] to distinguish collision-began from collision-cleared."""
+        if callbackfct not in self._collision_callbacks:
+            self._collision_callbacks.append(callbackfct)
+
+    def register_status_callback(self, callbackfct):
+        """Register a function called on EVERY gpio frame (async events and
+        /gpio_get responses alike) with the merged status dict."""
+        if callbackfct not in self._status_callbacks:
+            self._status_callbacks.append(callbackfct)
+
+    # ─────────────────────────────────────────────────────────────────
+    # Query / configuration
+    # ─────────────────────────────────────────────────────────────────
+    @staticmethod
+    def _extract_gpio(response):
+        """Unwrap a post_json return into the "gpio" dict.
+
+        mserial.sendMessage returns a LIST of response dicts on success
+        (self.responses[qid] is a per-frame list), a plain string on
+        timeout/interrupt, or an int qid when getReturn=False — so handle
+        all shapes defensively."""
+        candidates = response if isinstance(response, list) else [response]
+        for item in candidates:
+            if isinstance(item, dict):
+                gpio = item.get("gpio")
+                if isinstance(gpio, dict):
+                    return gpio
+        return {}
+
+    def get_status(self, node=None, timeout=1):
+        """Poll the collision detector (SDO reads on the CAN bus).
+
+        Returns the "gpio" dict: mean (rolling average), filtered, raw,
+        baseline, sigma, mode (0=auto/1=manual), reference, threshold,
+        sensitivity, trip, estop."""
+        path = "/gpio_get"
+        payload = {"task": path}
+        if node is not None:
+            payload["node"] = node
+        r = self._parent.post_json(path, payload, getReturn=True, timeout=timeout)
+        gpio = self._extract_gpio(r)
+        if gpio:
+            self.status.update(gpio)
+            return gpio
+        # Response didn't parse (timeout/odd shape) — fall back to the cache
+        # maintained by the async serial callback, which sees every frame.
+        return dict(self.status)
+
+    def _act(self, node=None, timeout=1, **fields):
+        path = "/gpio_act"
+        payload = {"task": path}
+        if node is not None:
+            payload["node"] = node
+        payload.update(fields)
+        return self._parent.post_json(path, payload, getReturn=True, timeout=timeout)
+
+    def set_threshold(self, threshold, node=None, timeout=1):
+        """Deviation band (ADC counts) around the reference outside which a
+        sample votes for "collision". Persisted in the slave's NVS."""
+        return self._act(node=node, timeout=timeout, threshold=int(threshold))
+
+    def set_sensitivity(self, sensitivity, node=None, timeout=1):
+        """Number of CONSECUTIVE out-of-band samples (at 50 Hz) required to
+        trip — and in-band samples to clear. 3-4 rejects single-sample spikes
+        while confirming a real collision within ~60-80 ms."""
+        return self._act(node=node, timeout=timeout, sensitivity=int(sensitivity))
+
+    def set_reference(self, reference, node=None, timeout=1):
+        """Explicitly set the idle baseline (ADC counts). Typically you poll
+        get_status()["mean"] while the system is idle and write that value
+        here — or simply use calibrate()."""
+        return self._act(node=node, timeout=timeout, reference=int(reference))
+
+    def calibrate(self, node=None, timeout=1):
+        """Tell the slave to take its CURRENT rolling mean as the new
+        reference (persisted in NVS). Do this while the system is idle and
+        collision-free."""
+        return self._act(node=node, timeout=timeout, calibrate=1)
diff --git a/uc2rest/motor.py b/uc2rest/motor.py
index d60c6ff..8653dfb 100644
--- a/uc2rest/motor.py
+++ b/uc2rest/motor.py
@@ -1098,7 +1098,7 @@ def set_joystick_direction(self, axis, inverted=False, timeout=1):
         '''
         if type(axis) != int:
             axis = self.xyztTo1230(axis)
-        
+        # {"task":"/motor_act", "joystickdir": {"steppers": [{"stepperid": 1, "inverted": 1}]}}
         path = "/motor_act"
         payload = {
             "task": path,