Besides my Swiss Army knife, this keychain LED is the most useful tool I own.
I use it to make my way a the battery lights.
They have two Lithium batteries and a switch to keep them on. Cost is $1.00 from Best Hong Kong. If you buy 1000 of them price is $.50
Just the batteries from Rat Shack are many many times the $1.00 cost.
They have a flat on one side very conducive to putting a sticker on.
Y11-08-29