Hammerhead Karoo Setup Guide

Use your Apple Watch as a heart rate monitor with your Hammerhead Karoo. Karoo has no dedicated companion app competing for Bluetooth — which makes this the simplest setup of any major cycling computer.

What You'll Need

  • •Apple Watch (watchOS 8 or later)
  • •iPhone (iOS 15 or later)
  • •HRM app installed on both Apple Watch and iPhone — download here
  • •Hammerhead Karoo 2 or Karoo 3

Hammerhead Karoo Compatibility

Can connect
  • Karoo 3
  • Karoo 2
No phone connection limitation. Karoo has no dedicated iPhone companion app that competes for Bluetooth. No workarounds needed — this is the easiest cycling computer to set up with HRM.

Full compatibility list →

Initial Setup

Karoo pairing requires a Bluetooth pairing confirmation on your iPhone — have it nearby.
  1. 1 Open HRM on your iPhone and Apple Watch, then press Start on the Watch.
  2. 2 On your Karoo: go to Sensors → + (add) → Add Bluetooth Sensor.
  3. 3 HRM App will appear in the list. Select it.
  4. 4 On your iPhone: a Bluetooth pairing request will appear. Press Pair.
  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 HRM — Karoo will try to use whichever sensor is active.

Setup for Every Ride

After initial pairing, Karoo reconnects automatically. The per-ride procedure is as simple as it gets.

  1. 1 Open HRM on iPhone and Apple Watch, then press Start on the Watch.
  2. 2 Karoo connects automatically. No need to navigate any menus.
  3. 3 Ride.
  4. 4 After your ride: press Stop on the Watch and terminate HRM on your iPhone.

If the Connection Drops

  1. 1 On your Karoo: Sensors → delete the HRM App 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.
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