Bluetooth
Bought a cellphone with Bluetooth, can ride my bike with the thing in my ear and initiate calls, answer calls, hang up, redial, with one finger. Oh, and talk and listen.
Can leave the cellphone in the living room, and wander all over the house using the same earpiece with microphone.
Phone has a surprisingly good camera, can download into my desktop by punching 2 buttons.
Maybe everyone in the world knows this already, but if anyone doesn't this is easy, convenient, cheap and effective. Possibly the only thing I've encountered which lives up to it's hype.
Arf