Accelerometers are a no hoper. As is any gps based method given the signal reception issue. tbh I really can't think of any foolproof passive method.
Best from a technological point of view would be an active system. e.g., off the top of my head, maybe a low power inhibition signal in the cabin, or a 'turn off' signal in the airbridge, coupled with a 'turn on' signal during offloading. But even then you'd have to give the device a manual override, for emergencies or company mobiles or just to make sure a device didn't end up disabled by accident. So people would override it anyway. So you might as well not bother (because you'd need worldwide cooperation by airports and carriers).