The keychain is a 125KHz ID card which can be repeatedly copied, erased and written. 
It also can be written with an HID number. 
You can use it for door access, elevator access, parking and other fields.

Specification:
1. 100% brand new and high quality
2. Frequency: 125 KHz
3. Thickness:4mm
4. Size: 35mm x 28mm x 4mm
5. Package included: 50pcs RFID Writable Keyfobs.
6. Material: PVC
7. Working Mode: Read-write modes - Can be used in 125KHz RFID card Copier/ Duplicator
8. Storage Capacity: 330 bit (264 free bit availability)
9. Reading distance is 0 - 10cm 

Packaged included:
10*Blue T5577 Keyfobs
10*Black T5577 Keyfobs
10*Green T5577 Keyfobs
10*Red T5577 Keyfobs
10*Yellow T5577 Keyfobs