While I am working my way back to full flights I have been doing short timed runs. I've been doing some maneuvers and needed a way to know when it was going to time off. I tried a small handheld unit that was OK to see the time but the alarm was not loud enough for me to hear when concentrating on the flight. By chance my wife was using her iPhone timer and the alarm was pretty loud. I tried this today with my iPhone and was able to hear it and feel it in my pocket. Works really good even on my weak side.
Best, DennisT