How fast does Michael Phelps’ heart beat under water? In the past, Phelps would have had to check by stopping mid-stroke and checking a small screen on his wristwatch. But with the launch of the AquaPulse from Finis, Phelps can receive real-time audible heart rate updates, without coming up for air.

The AquaPulse ($139.99), available in July, uses an infrared sensor attached to an athlete’s ear lobe to monitor heart rate by quantifying light pulses due to capillary blood flow in the skin. That data is then communicated audibly to the swimmer by way of Finis’ patented bone-conduction method, utilized in its SwiMP3 music player. Instead of fiddling with earphones that won’t stay in place, bone conduction actually transmits vibrations through the temple bone and into the inner ear. According to Finis, the presence of water, and not air, makes the sound quality of bone conduction even better than the sound quality in traditional ear-buds. The entire gadget is just 3.5 inches wide by 1.5 inches long, only half an inch thick. It clips onto a swimmer’s standard goggle straps.

The AquaPulse ensures swimmers follow their precise workout regimens, only tapering or pushing it at the appropriate level. Data is communicated in beats per minute based on the average of ten second samples. Swimmers can adjust the device in order to receive updates at a variety of intervals (20 sec, 30 sec, 45 sec, 1 min, 2 min, 5 min) or get an instant update by pressing a button. A single charge through a USB connection provides eight (or more) hours of run time, so there’s no excuse for skipping out on endurance training. For those not wanting to give up underwater musical beats to stay on top of their heart beats per minute, hold out a bit longer – a combination of the SwiMP3 and AquaPulse is in the works.