The Basis B1 watch is like many other fitness monitoring devices currently vying for the wrists, necks, waists, and chests of fitness oriented customers; the watch is equipped with sensors monitoring commonly tracked physical parameters: a 3-axis accelerometer for movement, a perspiration monitor, and even one for reading skin temperature throughout the day.
The fourth sensor is the most interesting: an optical blood flow reader, which offers wearers the ability to pull up a heart rate reading from their wrist without the slightly burdensome addition of a chest strap. The sensor measures blood flow via the capillaries underneath the skin of the wrist using a bright green light emitted from the underside of the watch.
The tradeoff is the unit isn't really designed as a device to track exercise during workouts. Where the $199 Basis B1 shines is as a health tool for tracking the arguably more important health analytics recorded throughout the day away from activity/exercise, continually monitoring the wearer's vitals, and recording day-to-day patterns, including total steps taken, calories burned, duration of sleep, times awoken, and overall sleep quality. In this way, the B1 is more of a long term accomplice to a heart rate monitor, which works best for real-time feedback during more strenuous exercise activities. B1 users are able to access and review their overall health analytics via website only after syncing wireless via iOS or Android app, as the display itself is quite basic.
There's a fantastic in-depth review of the Basis B1 over at DC Rainmaker for those seeking how the device stacks up to the likes of the Fitbit Zip and the Withings Pulse, including detailed analytics graphs and the caveats/compromises connected to using the B1.
For now, after reading about the deficiencies still inherent with the strapless wrist design, I still plan to continue to use the Nike+ Fuelband for daily activity recording, and don the chest strap for running and while at the gym. But I do look forward to a near future when streamlined wristwatches will do it all and I can put away the strap.
Other strapless wrist heart rate monitors available today:
(Images: Basis; as linked above)