WG,
I swear by
this watch by Casio. The watch has a vibrating alarm, so there would be no need for you to constantly look down to see remaining time or worry about being able to hear an audible alarm. Also, you can set various intervals, so when I work BJ at a stadium with no 25-second clock, I set Interval 1 for 15 seconds and set Interval 2 for 10 seconds.
I don't know if that watch is still available or not, but if so I would highly recommend it.