The Temp Trainer Pro from Finis is an audible metronome pacing device that can be used by swimmers to set a pace for their swim stroke and eliminate lulls in their swim. This small, lightweight Tempo Trainer fits easily under a swimming cap and uses beeps to set an ideal stroke rate. It will help increase consistency by using the beep which can be heard in and out of water so you can find your perfect pace.
Yep it works very well even though I can never remember which buttons do what, it's easy enough to try them all until you get it! It's certainly loud enough to work well to improve stroke rhythm.