A window sensor with a sound alarm is actually pretty useful. It gives you an instant alert if someone tries to open the window, and the loud beep alone is usually enough to scare off anyone who isn’t supposed to be there. It’s also one of the easier security add-ons to set up, so you don’t need a full alarm system just to cover one weak spot.
It helps for peace of mind too, especially if you’re out a lot or you have kids at home. The only thing to watch out for is making sure it’s installed right, because a loose sensor can trigger false alarms. But when it’s set up properly, it does its job well.