>Maybe something like a soft object that when a few moments after it is released makes a squeak sound.
Could use some kind of heat or capacitive touch sensor to detect when it's no longer in contact with your hand. Or I guess the KISS version of that would just be to use some sort of physical switch to detect when the object hits the floor. I could totally see there being a market for something like this!
I spent a bit of time trying to do it with flex sensors. Strap one to your hand, make a fist, take your nap, detect when muscle tone is lost and it unbends. I ran out of interest before I got it to work but I still think it's viable. Probably smart to build the flex sensor into a glove for ease of use, and you could put the microcontroller on there too.
You could also buy one of those two-piece door sensors that sound an alarm when you separate them. Tie one to your hand (or glue it onto a special sleeping glove), and hold the other piece.
Only potential problem is that you might get a heart attack considering how loud those things can be.
Could use some kind of heat or capacitive touch sensor to detect when it's no longer in contact with your hand. Or I guess the KISS version of that would just be to use some sort of physical switch to detect when the object hits the floor. I could totally see there being a market for something like this!