[spdustin]

Vibration sensors usually emit X/Y/Z magnitudes, and are small enough to attach to a collar or possibly vetwrapped to a leg (if he'd tolerate that). I haven't used any of the Bluetooth LE ones, but I do use a Zigbee vibration sensor from Aqara (https://www.amazon.com/dp/B07PJT939B)

You'd need more infrastructure (like Home Assistant + a Zigbee dongle, or an always-on app listening for BLE advertisements, depending on the sensor radio) but you could apply some filtering to a vibration sensor to determine a threshold for alerts.

(despite the description saying you need the Aqara hub, the sensor works with most Zigbee coordinators, and certainly the popular ones in the Home Assistant community.)