So I guess you could try the vibration sensor route, but they are kinda tricky to use. (I know it's a totally different purpose, but lots of people have tried to create laundry automations with these with mixed luck. Power monitoring is certainly better. Easy if yours plugs into a receptacle...less easy but not impossible if it's hardwired.) The SmartThings Mutli isn't super-expensive (I think something like $20 list but they're on sale for less now), and you'll at least get a decent contact and temperature sensor out of it if your experiment fails. I haven't used one for vibration so can't speak to how sensitive it is in that regard.
Regardless of what device you use, since this use is important to you, I'd consider something like Device Watchdog to monitor/guess if this device falls offline. I guess you'll probably know since the point would be to notify you if it doesn't detect vibration or a certain wattage or whatnot in a certain period of time (something that would also certainly happen in this case...unless it falls off while active or in use and you don't also monitor that for suspicious activity, I guess), but it's a neat app to have regardless. 
