How do I know that base is online?

Your base station is online when all three lights (LEDs) light up. If this isn’t the case, you can find out here what the reason could be. You can also look under SYSTEM OVERVIEW in the app to see if base is online. Simply click on base and then on HELP.

If a sensor is online, its LED is off. If the LED is flashing, the sensor is outside the range of base. If the sensor's LED is off, but the sensor is shown in the LED as offline, it is very likely that the batteries are flat.