ETEKJOY 10 PCS Writable 125kHz RFID Sticker Coin Adhesive Back T5577 Proximity ID Card Token Key Tag Rewritable Dia 25mm (Blank Card No Data)

Only one entrance to my building can be opened without a key fob, and I hate carrying it with me since my unit has a smart lock. My solution was to use a Flipper Zero (there's another review that said it doesn't work, but it definitely does) to clone the data from the fob and write it to one of these. I stuck it on the back of my phone with super glue (the adhesive works well but obviously wasn't designed to be used like this) and have been using it close to daily for about nine months and have never had an issue. Only slightly annoying thing (not the sticker's fault) is every time I hold my iPhone up to the reader to scan the sticker, the wallet app opens automatically—if you don't want that to happen, you need to disable express transit/payment in the settings app. Overall would highly recommend!

Doesn’t work

Update: I did notice one issue with this RFID (as well as with other types that are based on same T5577). It programs well and reads back correctly, identical to the original tag. However, in one office setting, I noticed that the programmed tag is recognized properly by all door readers, but not by the readers on the elevators. This is quite odd that Proxmark is not picking up the difference between the original and the programmed one. Somehow none of these tags were recognized by the elevator. Interestingly, I was able to find one type of tag that appears identical to how it handles the programming but also is recognized by both door and the elevator readers. Something to keep in mind that the programmed tags could have a small chance of compatibility issues. There are two common standards that I've seen around for doors/garages/offices in the 125kHz frequency: HID and EM4100. The first one has two identifiers facility code (fc) and a card number (cn). The second one is just one number. These cards can be programmed to emulate either of the standards. Programming these cards requires some kind of programming device. I had one old hand-held that can only read EM4100 and is easy to use: push the read button, scan a source card, push the write button and put it next to the writable card. Putting the Etekjoy cards for the writing process successfully duplicates the card and now you have two identical cards. Programming the HID standard (typically the cards that have "HID" embossed on them) requires a reader/writer that understands those, like Proxmark3. If you know the facility code and the card number, the command "lf hid clone -w H10301 --fc 123 --cn 12345" will program these Etekjoy cards and you have a duplicate that will read well in other readers. I really like the small size of the card and the fact that it has a adhesive back. It can be attached to the back of the phone inside a case, for example. The card is not flexible and you have to account for the 1mm width. The cards cannot be read without programming first. Each card being under a dollar is a great value.

Compatible for HID, Accurate description. Great product

They don't write. Had to buy something else.