I use a free app on my Android phone called "StopWatch & Timer" made by sportstracklive.com. It has two functions - stopwatch and timer (who'd've thunk it?!). It's got nice big numbers and touchscreen controls... and this is a little detail, but you can make it be any color you want. I mean, I just use black background with white numbers for ease of vision in the dark, but it's nice knowing I could make it bright pink if I wanted, haha. I use the stopwatch for timing runs, pressing the lap button to break down the times for acts or whatever else you need times for... And during rehearsals, I use the timer to keep on top of the 80/10s (or 55/5s). The stopwatch functions are all silent, and the timer has alarm options but you can set it to have no volume, so all it does is vibrate twice. It's really non-intrusive. The app requires no internet or data, so it works while the phone is in airplane mode (or as I like to call it, performance mode). Oh, and you can pre-set multiple timers, so as soon as the 80 is done you just switch to the 10 minute one, and then back at the end of the break.
Last week during a performance my book started to slip off my music stand, because I'm an idiot. So I reached out to grab it, and knocked my phone off the counter, and it fell on the floor and the battery fell out. Okay, not the end of the universe, because I already have my up time noted so I'll just figure out what was lost, and it won't be perfect to the second but oh well. Not really the end of the universe if I guess and am off by 30 seconds, right? So I wait til I have a breather between cues, and I grab my phone and start to put it back together. It turns on, but the stopwatch app isn't found, because it lives on my SD card which had also gotten knocked loose during the fall. So I jiggled the SD card and tried again, and pulled up the stopwatch and it was still running accurately. As I was loading it up I wrote myself a note to add exactly ten minutes to the top of the time because that's what was lost... and then I opened the stopwatch and it read 10:22 and still counting.
I have no idea how this happened, and I'm sure if I tried to recreate it, it wouldn't happen again. I mean, the app is stored on an SD card and the SD card was removed! So this is probably some once in a lifetime anomaly, but... it was pretty dang cool.