I'm posting this information here largely in case I need to find it again at some point, but also because it might be of interest to someone else.
At a major event that we hosted a few months ago, we were getting things set up on Friday for the start crew, and the question came up of what we had in the way of clocks (since everything had been shut down for a couple of years, it was unclear where some of the equipment was). We rustled up a couple of "atomic clocks" (medium-sized digital clocks that auto-synchronize) to display the time, but somebody asked about clocks that could do a five-second audio countdown every minute or two minutes or whatever. The club used to have some custom-made analog clocks that would do that, but they were delicate and nobody could remember having seen them in years. Somebody else said "can't we do that with a phone?", and of course the answer was yes, it's 2021 and of course we can.
I spent a few minutes that night cobbling together an acceptable solution (there are probably many such solutions, some no doubt better, but this one was good enough). I have a couple of retired Android phones on the shelf, so I fired one up, turned on the wifi so I could load a new app, found and installed one, and configured it.
I actually tried a couple of free apps, and the one I decided on is called Interval Timer
. Here's the information and the way I configured it, for future reference. This configuration does a five-second audible countdown every two minutes, and runs for five hours. Starting it is a little tricky, you have to hit the start button one second before the minute, and it might take a few tries to get it right.
We paired the phone with a portable Bluetooth speaker to provide more volume, and I also had a USB recharger battery plugged into the phone since I couldn't remember how good the battery life was on it. (I had turned off wifi and mobile data to minimize power consumption.)