Under Armour Armour39
BEST FOR: Leaving the Phone at Home
The 39 ($100) stands out from other heart-rate monitors in two important ways: internal memory lets you forget about your iPhone during training (sync later via the UnderArmour or MapMyFitness apps), and a precise monitor captures average pulse and also parses when you’re ramping up intensity or in a rest phase, critical for accurate interval training.
TomTom Runner Cardio
BEST FOR: Consolidating Your Devices
This integrated watch, GPS, and heart-rate monitor ($270) reads your pulse from your wrist using a sensor built into the back of the watch body, meaning no more unwieldy chest straps. We were impressed with the amount of technology on board (it tracks pace, distance, heart-rate zones, and calorie burn) and loved that it sent data directly to our favorite fitness apps when synced with our phone.
BEST FOR: Working Across Platforms
Most gadgets talk to each other using either Bluetooth or ANT+ radio waves. The impressive Viiiiva ($80) uses both signal types, allowing you to use this heart-rate monitor with everything from mobile apps to watches and computers. It can also gather data from multiple ANT+ sensors and send it to a Bluetooth device, turning your phone into a true fitness computer.