I am trying to troubleshoot a new Bluetooth heart rate monitor that is attached to a chest strap. When I try to scan for Bluetooth devices with my computer or Android phone, it does not show up. There are no lights or buttons on the device and I want to make sure I have it turned on. Therefore, I'm trying to figure out how does it turn on?

The instructions say to

  • Wet the chest strap
  • Snap the heart rate monitor to the chest strap
  • Place the strap around your chest

Is it turned on when it's snapped to the wet chest strap? I.e., is it activated when there is a conductive path between the two buttons on the sides of the device (via the wet strap)? Is there a conductive path if the strap is dry?

Is it turned on when it's strapped to your body? Does the monitor's circuit somehow pass through your body? Does the device need to sense a pulse to begin transmitting? Does it rely on detecting an electromagnetic field that is only achieved when the strap is against your skin?

Out of curiosity, does anyone know how these devices detect heart beats? Is the device sensing the electrical current that causes your heart to contract? Is the device sensing the electromagnetic radiation from this electrical current? Is it sensing the pressure from a heart beat?

The device in question is a Polar H7


2 Answers 2


The strap has two areas that measure the heart rate by measuring the bio-electric impulse that naturally occurs when your heart beats. The strap itself is the measuring device, and the pod you snap on collects the impulse and transmits it to a receiver. The monitor begins its job as soon as the buttons are snapped in. In short, the strap does not need to be wet to measure your heart rate.

The moisture improves the sensitivity of the heart rate monitor giving it a more accurate result. Wetting the strap before exercise allows you to enjoy the same level of accuracy before you raise your heart rate and sweat.

  • Thank you. So leaving the transmitter snapped to the strap will likely drain the battery?
    – drs
    May 1, 2013 at 17:10
  • 2
    Correct. Snapped in is what completes the circuit. May 1, 2013 at 17:25

They are activated when wet. The best and most effective way I have found to get it to turn on and connect is to run under a faucet for a few seconds. Get it real wet and you should be good to go.

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