The Honeywell 300-07753 is the UL-Listed 9VAC transformer designed to power the Honeywell 5800RP wireless repeater. Originally the Honeywell K10145WH was the transformer for the 5800RP. However in October 2015, Honeywell released the 300-07753 to comply with new UL listing requirements. It is still a traditional 2 prong 9 volt AC power adapter except they added a green status LED to determine if the transformer is on or off. The 5800RP is a repeater that will double the RF range of any 5800 series sensor. It comes equipped with the K0257 backup battery but it requires AC power from this transformer to remain powered on. In the event of AC loss it will pull power from the internal backup battery.