Garmin's new Index Sleep Monitor fits around the arm to track breathing variations, sleep stages, heart rate variability, skin temperature and more.

Garmin's latest wearable is the Index Sleep Monitor, a band for overnight sleep tracking that means you don't need to wear a watch in bed.

Garmin Ltd. on Wednesday launched an arm band for wear during sleep that can track vital health metrics, stepping up competition with companies like Whoop Inc. and other emerging players.