Devices monitor health from your wrist or pocket

For the past few weeks I’ve been testing three different devices designed, in part, to measure health and fitness. Two of them, the Apple Watch 4 and Fitbit Charge 3, are watches.

The other, called Kardia Mobile, is a tiny $99 device that can easily fit into a pocket that you pair with a smartphone.

The Apple Watch, which starts at $399, is a full-featured smartwatch. It not only has lots of features built in but also supports third-party apps, similar to the iPhone.

The Fitbit Charge 3, which sells for $149, is billed as a fitness band, but also has essential smartwatch features including text, email, calendar notifications, timers, alarms, weather information and an app designed to help you relax.

The Kardia Mobile and Fitbit devices work with nearly all smartphones. The Apple Watch requires an iPhone 5 or newer.

What the Kardia Mobile and the Apple Watch have in common is the ability to record electrocardiograms and measure for atrial fibrillation (AFib), a potentially dangerous heart condition that can be a precursor to a stroke. Apple announced that it would be adding the feature to its Apple Watch 4, which reportedly is part of an update rolling out right now.

Before I get into my review of these devices, I think it’s important to shed some light on the issue of who should be using devices like this to monitor their condition.

I’m not a doctor and clearly