Help with Special Training

I'll be attending a long-play tournament later this week, and to practice, I'll be using physical pieces, and playing OTB against friends and family.

To help my mental endurance and to help me make proper use of my time, I plan to use -some kind of device- to make a small sound (like a beep) every three minutes, as I'll have roughly 3-6 minutes per move to calculate during my actual tournament matches.

Do any of you know of a website or an app that could perform this feat?

http://www.online-stopwatch.com/interval-timer/

Something like that would work. Just add an interval for 3 minutes then select restart when done so it starts counting down again after every alert.

@NeverBeenTimid
Perfect! That sounds like exactly what I was looking for.