Issue duplicating EM4100 RFID fob to cards I brought

I have a cheap home alarm system which came with a couple of RFID keyfobs which can be added to the alarm system to make it easy to disarm/arm it. One of the first thing I did is use my flipper to read and store one of these fobs. I then decided to buy a pack of RFID cards online so I could play with duplicating what I had saved here.

The keyfob that came with the alarm detects as a EM4100 and if I replay the card it works just like the fob and disarm/arms the alarm when used. Yet I cannot seem to write what is saved from the keyfob to the cards I bought online which are also EM4100. I thought maybe the cards I got are not writable, but I’ve tested those by reading one and writing onto another. It seems like the format of the keyfobs that came with my alarm are different and cannot be written to the cards I bought online. This despite the online store listing saying they are eeprom, which I assumes means erasable/reprogrammable.

Also, the cards I got online can be added to the alarm system and are supported. Yet I cannot copy the fobs that came with the alarm. This issue must exist in a lot of cases really where the cards one has read and saved won’t write to other cards which are also EM4100. I think it is also possible this is some kind of bug.

I have included redacted screenshots below of the fob (which goes on my keyring) and the card below…


Edit: further tests reading one of the cards I got online to another show they are not properly writable. I think I have bought the wrong thing here, I would delete the post, but instead I ask where do I get cards compatible like this that are writable?


In my initial tests of the cards being writable I was writing one card back onto itself, and I think the Flipper in this case reads the same value back and assumes it is written. A good feature would be to warn about this kind of duplicity.

EM4100 cards are not re-writable. They can be added to existing alarms, but this is the alarm system recording the code from the cart to its memory. You need a T5577 card to clone other cards to it.

Also, there is no way to check if we are just writing to a non re-writeable card with the same ID or we have successfully cloned the card due to how RFID writing works.

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Thanks Astra, I’ve ordered some T5577 cards online, and they sound like what I need. I am marking your post as an answer. I’ll come back to this thread if I run into any more issues.

It sounds like the Flipper should warn users about trying to write to a non-writable card.

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It does warn you, you’ve even attached the photo of the warning :slight_smile:

It just says its been taking a long time to write. It could read, detect EM4100 and say “This device is not writable.”

It is impossible to differentiate between locked and non-writeable cards due to how LFRFID works. The only thing you can read from a card is its ID, and it doesn’t say anything about what type of card it is, except for the protocol it uses. You can have a EM4100, a EM4305 and a locked T5577 set to EM mode and you wouldn’t be able to tell which on is which without a successful write.