Need to decode keeloq serial numbers

[Nigel Johnson]

Hi, I volunteer in our condo, and we have a couple of Door King receivers, each with 100 memories. Our super has loaded new serials without deleting, so it is now full and we cannot add any more.  I want to be able to decode serials when people show me their fobs, so I can find out whose fobs are active. Most of them have missing labels, they are so old :-) 

I installed rtl_sdr and rtl_433 and it successfully reads a fob press and correctly identifies it as coming from the HCS200 chip inside, but it gives an ID in hex which, when converted to decimal, bears no resemblance to the fob's serial as shown on the label.  It also reports an encrypted value which is no use to me.

The data sheet from Microchip says the serial number is sent in the clear.

Does anybody know how to extract this?

[Benjamin Larsson]

Hi, can you get a fob with a label and then record the signal when the
fob is activated? (-S known) That way we might be able to figure out the
serial encoding.

MvH

Benjamin Larsson