The very popular RFID cards, are read-only, containing a unique serial number (UID) for the purpose of identification, like access control, time and attendance or other applications where it is not required a high level of security.
 

Manufacturer:	EM
RF protocol:	EM4100 / EM4102 / EM4200
Frequency:	125 kHz
Memory:	64bit - Read only memory
Modulation:	ASK
Reading distance:	2-3 cm
Dimensions:	CR80 (85,60 x 53,98 mm)
Thickness:	0,84 mm
Material:	PVC
Printing options:	offset, thermal re-transfer, thermal transfer