Suggestion for program

@allObjects, @Gordon Thank you for your great responses.

I have settled on using the light sensor, as the puck will be inside the tub, and will get flooded with light when he opens the lid.

Problem is distance. Gordon, how far should I expect a puck to Rpi to be able to communicate?

What I usually say is to transmit a number all the time, and to then just increment that number when something happens.

Isn't that going to burn up the battery? I would like to get a couple of months battery out of a once a day event advert.