Use of bluetooth-connected devices (except external GPS units) is fully functional in Locus Map Pro only. In Locus Map Free, it is limited to 10 minutes.
Menu > More functions > Bluetooth manager
Locus Map can communicate with various Bluetooth-connected external devices - external GPS units, heart rate monitors, bicycle speed&cadence sensors, Zephyr sensors, Polar sensors and NMEA readers. Bluetooth manager displays their switches and settings.
List of tested and supported devices is available HERE >>