Sportacus' crystal

From LazyTown Wiki

Sportacus' Crystal is a magical crystal of some sort that warns him when someone is in danger by beeping and glowing.

As seen in Crystal Caper it works with anyone and even when the actual possessor is the one really in trouble. The Crystal is never seen working when Sportacus knows that someone is in trouble, or gets in trouble himself, so, apparently the Crystal doesn't warn Sportacus when he knows that someone is in trouble.