As far as I can see, its the receiver for a wireless thermostat. I would hazard a guess the CH1 button is some kind of manual override and the PROG button is just used during installation/commissioning, to pair the RX-1 and the corresponding thermostat transmitter. You may be able to confirm all that from the datasheet, catalogue sheet and the manual for the Danfoss RX-1.
Copy this link and paste it into your browser:
https://store.danfoss.com/gb/en_GB/Climate-Solutions-for-heating/Electric-Thermostats/Accessories/RF-Receivers/RX-Receiver%2C-RX-1%2C-1-ZONE-RECEIVER-433-92-MHZ%2C-230-V%2C-SPDT/p/087N747600#productReferencesProductObsoleteReferencesComponent
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November 2021
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