I do not know what it is called exactly but we have these little small carry oven timers.
No access but you can memorize where the buttons are and keep on starting it at the time you set it up for.
It beeps like crazy until you go and hit stop. And it is ready to start again if you hit the start button.
Sometimes I use it myself just to keep myself from getting lost in space and losing track of time. Like to set for every 30 minutes or so.
Flat little things about the size of a credit card. They have a belt clip on them. Pretty handy. At kitchen stores I think is where my wife got it.