Question:
With the change from savings time to standard time, we are reminded to not only change our clocks, but also to change our smoke detector batteries. I assume this is one of those 'better safe than sorry things', and that if you really changed the batteries every 6 months, you'd be sure the batteries were good.

My question is, since I have a volt-meter, what voltage is sufficient for operation? Or, should I do the suggested replacement every 6 months?

Answer: Alas, checking a battery's state of charge isn't quite that simple. For the major portion of its life, an alkaline battery puts out a steady voltage (and the related amperage..).

So a simple voltmeter check will pretty much show full voltage for the first 90% or so of the lifespan. It's only at the tail end that you start seeing useful changes. (And by then all currently certified smoke detectors will give you the chirp-chip indicator)

There are some tricks you can do which involve placing differnet loads on the battery and charting out the voltage drop at each set point, but that's not as simple as one would wish and you need a reference chart..