Garmin HRM sensors

The the following Garmin HRM sensors only use ANT+ for communication:

Since the iPhone does not have the hardware necessary to connect to ANT+ devices, the only way to receive a signal from these sensors is to use additional hardware. Heart Graph can connect to the Wahoo Fitness Key for ANT+ sensors, although this is for the old 30-pin iPhone connector.

Note that the Garmin HRM-Dual, which supports both ANT+ and Bluetooth transmission simultaneously does connect to Heart Graph directly.