I bought a kitchen timer for 650 yen ($6.37 €4.74) at a supermarket Life.
My son loves to do TV games on his tablet PC. He always plays them endlessly. So we set the time limit of playing TV games. He cannot play the game beyond two hours a day. To time the playing time, I bought the kitchen timer.
When he plays a TV game, he set the timer and ends up the game when the alarm rang.