https://forums.garmin.com/showthread.php?313424-Firmware-Version-5-20-Now-Available!
If your device did not automatically prompt you for this update, (requires that Wi-Fi feature is enabled) it can be downloaded by using Garmin Express. Please note that once a software update is released it can take up to 24 hours before Garmin Express provides this update to all users.
Changes made from version 4.20 to 5.20:
Added HRM-Tri and HRM-Swim support.
Added Connect IQ 1.1.3 SDK support.
Added tone-only and vibration-only options to the alarm.
Added a shortcut for changing the pool size to the shortcuts menu in a pool swim activity.
Fixed a crash that could occur when uploading an activity to a paired smartphone over Bluetooth