Waldbeck Halley Mode D'emploi page 53

Install Batteries
Insert 2XAA batteries in the battery compartment. The LED indicator on the
back of the transmitter will turn on for four seconds and normally flash once
every 16 seconds (the sensor transmission update period).
Figure 6
If no LED light up or is lighted permanently, make sure the battery is inserted
the correct way or a proper reset is happened. Do not install the batteries
backwards. You can permanently damage the outdoor sensor
Note: We recommend lithium batteries for cold weather climates, but
alkaline batteries are sufficient for most climates.
Figure 7
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