Dual Frequency RFID Key Fob 125Khz EM4100 and 13.56Mhz MIFARE Classic 1K Chip (Pack of 10) (Black)

They seem to work!!

They work but they don't seem as reliable as others we have and are kind clinky, meaning the plastic they are made from makes a lot of noise hitting against my keys

They don’t work! Emailed support and they were not any help.

The fobs I received are just as pictured in the add except that the numbers are printed instead of etched as they appear to me in the add. These are read only devices and you can't reprogram the numbers. The device I ordered them to work with utilizes 125khz EM4100 and 13.56Mhz M1 frequencies, and it was able to read these fobs exactly as expected. The fob must be within about 2 inches of the reader before they register and to date every reading has been accurate. The fobs are very light and hollow, but they can be squeezed pretty hard without issue. The cases are pretty strong, so risk of cracking appears low. Since I only just received them, I can't say how well the two halves will stay together over time. The printed numbers may wear off, but since the fobs are scannable that is not of much concern.

This may be dual frequency but it's not the two frequencies listed in the description. I was able to write the 13.56 to it but not 125Khz so they were no better for me than single frequency but clunkier.