Place the Health Tag from Spire on your underwear and track heart rate, sleep, steps, and calories. But unlike other trackers, this one is meant to be concealed under clothing and has a battery life of 1.5 years. You’ll need to get a new device when the battery runs out, but the brand offers free replacement. Additionally, the Health Tag is waterproof, washer-dryer safe, and syncs with an app to view health insights. Check out Spire’s site to grab one tag for $49, or a three-pack for $99.