The strap wraps over the device, but since there’s no display, that’s not a problem.

It has a hemispherical silhouette: an inner flat side with sensors that presses against the skin, and an outer curved side with prongs to hook into a wrist strap. The Amazon Halo hardware is a metallic capsule about the size of other fitness trackers. It’s a refreshingly minimalist experience. Like other basic trackers the Halo lacks vibration, so it can’t be used for reminders, notifications, or wake-up alarms. Rather than a shortcoming, this is the key to the Halo’s appeal. After that, you’re likely to forget it’s there, given that you won’t be looking at its screen for insights – instead, you’ll have to pull out your phone and switch to the Halo app for those. The Halo is comfortable enough to wear, though it’s a bit wide and can rub up against the wrist joint, and can require a little adjustment before it sits right. Given that there’s no display, the button is only used for muting your mic for privacy while using the optional Tone feature, which periodically listens to your vocal intensity and can be set up to nudge you when it detects you’re in a mood. The Halo is a screen-less tracker – it’s basically an oblong pod on your wrist with a single physical button, an LED light, and a microphone, with a fabric wrist strap wrapped over it (or rubber, if you opt for the fitness-type band).

Amazon halo blood oxygen