C4

Some sort of signal emitter maybe? So the rescue team knows to look where the hero rat triggered it.

I do hope it has a little speaker that says "don't worry human, help is on its way" in a cute high pitched voice.

Its little lunch and a sweater the doc packed in case it's cold.

My guess would be an accelerometer. Then you can plot out the mouses path and get the location of the person

Cheese