Hammerhead Karoo Setup Guide

AirHRM sends in-ear heart rate from HealthKit to your Hammerhead Karoo. No chest strap, no extra hardware. Pair it once and your Karoo reconnects automatically before every ride.

What You'll Need

  • •Compatible AirPods Pro with heart rate (see Apple’s specs; AirPods Pro 3 were the first with an in-ear sensor)
  • •iPhone with iOS 26 or later
  • •AirHRM installed on iPhone: download here
  • •Hammerhead Karoo 2 or Karoo 3

Hammerhead Karoo Compatibility

Can connect
  • Karoo 3
  • Karoo 2

Full compatibility list →

Initial Setup

  1. 1 Open AirHRM, insert your AirPods Pro (connected), and tap Start.
  2. 2 On your Karoo: go to Sensors → + (add) → Add Bluetooth Sensor.
  3. 3 AirHRM will appear in the list. Select it.
  4. 4 On your iPhone: a Bluetooth pairing request will appear. Press Cancel.
  5. 5 Your current heart rate now displays on the Karoo.
If you're also using a chest strap or another heart rate sensor with your Karoo, disable it in Sensors before connecting AirHRM. Karoo will try to use whichever sensor is active.

Setup for Every Ride

After initial pairing, Karoo reconnects automatically on every ride.

  1. 1 Open AirHRM, insert your AirPods Pro, tap Start.
  2. 2 Karoo connects automatically. No need to navigate any menus.
  3. 3 Ride.
  4. 4 After your ride: tap Stop in AirHRM and stop the session in AirHRM.

If the Connection Drops

  1. 1 On your Karoo: Sensors → delete the AirHRM sensor.
  2. 2 In your iPhone's Bluetooth settings: find "Karoo 2/3" and "Karoo 2/3 BT Audio" and select Forget. (This step is usually optional but helps if re-pairing fails.)
  3. 3 Re-pair following the Initial Setup steps above.

AirHRM Shows Heart Rate but No Connected Device

That is the expected state until a receiver connects. A live heart rate means the AirPods Pro side is working. The connected-device line only reports whether anything has picked up the broadcast yet, and it clears the moment your equipment connects. If it never clears, the problem is on the receiving side: pair again with AirHRM broadcasting and in the foreground.

iOS 27's GymKit update doesn't change anything here. See what it covers and what it doesn't

See AirHRM in action

Watch my AirPods Pro heart rate show up on Zwift and a Hammerhead Karoo — in under three minutes.

Ready to Ditch the Chest Strap?

Open AirHRM, AirPods Pro in, tap Start, and ride. Try it free for 7 days. No charge if you cancel before it ends.

7-day free trial
$7.99 / year

after your trial ends

Less than a 3-pack of batteries.

Download on the App Store

Cancel before the trial ends and you won't be charged.