Old, used CR123 batteries: flashlight (torch light)

Here's one way to use up the stack of old CR123 batteries that are half-used. (For example, proactively replacing smoke detector batteries)

Ener-gizer flashlight TAC..300 uses one CR123 battery. It runs for about an hour on the "low" setting on an old battery. Available at Homely Depo for $10, and at least one online place.