What is the device on the belt of basketball officials?

Does anyone know what the device is on the belt of basketball officials? I was at a men's and women's basketball game at Northern Illinois University yesterday and noticed all six officials wearing one. The other thing I noticed was that they would push a button on the device every time the ball was put back into play. Anyone know what it is?

It's so that when they blow they're whistle, the clock will stop.That's all. & they turn it back on when they give the player the ball.

a whistle