Polar’s OH1 is an optical heart rate monitor that is among the best when it comes to accurate heart rate readings. This small device is an affordable way to track one’s heart rate while working out, and it’s incredibly versatile. The OH1 can be strapped to the upper body or the forearm and can even be clipped to goggles while swimming so as to not get in the way. It can be used as a standalone device or be paired with smartwatches or other devices.