I use the Casio G Shock (model number ? ) . I set it for 20 seconds and it then beeps every second. I can switch to the stop watch for time outs. Nice feature is that the buttons are schrouded so bumping them will not stop (or start) the timer.
I checked other watches and the beeping was continues (beep,beep,beep...) Where the Casio is beep,beep...beep,beep...beep,beep...every second. Hope that this made sence.
I have been hit by players and the watch keeps going.