Remember back when transistor radios ran on 9V batteries? And now just about everything takes some lower voltage, and converts it up if necessary?
So now nothing around the house takes a 9V battery, except the smoke detectors?
... Oops. And my IR thermometer. Which, when I picked it up just now and pulled the trigger, squeaked plaintively and emitted a pair of dim, and quickly fading, aiming beams. Yup: dead 9V battery.
There's one spare 9V in the kitchen junk drawer, and it, as it turns out, is junk.
I'd order a batch from Amazon, but I need that measurement today, just to check on the new & improved temperature sensor on this board I'm bringing up. So, I suppose, off to a local store in search of an overpriced alkaline stack. There ought to be spares for the smoke detectors on hand, too, so I guess I'll look for a deal on a multi-pack.
Update: Buying 9V batteries locally turns out to be a Bad Deal. Fry's (which has more or less typical retail-store prices on such things; I went there because I also needed an Ethernet patch cable) had 1- and 2- packs, all significantly overpriced. Amazon turns out to have 4- through 12- packs at quite reasonable prices. But I bought one of the less-outrageously-overpriced 2-packs yesterday, so I'm set for now.