I locked my keys in the car so often (at remote job sites too) that DS made a belt clip for them, with a laynard just long enough to reach from belt to key slot with a little wiggle room left over.
Hose timer. I'm adding some wind-up (no battery) kind to set at each outdoor faucet to the next order to the drip irrigation company.
I set my cell phone alarm so often for different things, I forget what I am supposed to do when I hear it. (#1 wake up, #2 make sure kid makes school bus, #3 anything different, like leaving on time for appointments.) My ideal cell phone would have a dozen different programmable messages. Hmmm, maybe it does - have to ask the kids.
I would literally forget my head if it wasn't attached.