[Closed] stopwatch for interval training

Used to do intervals on my excercise bike a few years ago till I got rid of the hateful thing. 30 secs flat oot followed by 30 rest X5 sort of thing. I want to get back into it on a proper bike but find it impossible to look at a watch when I am exerting myself to the point of eye popping/nausea so I want something which will beep every 30 secs.

any recommendations for this? Had a look online and found one called the Gymboss. Looks like what I need but wanted to check here if anyone has experience of these things.