These are passive read only RFID tags. They hold a unique 64-bit number that can be read by an RFID reader. The frequency and protocol must match the reader you are using.

Unique 64 bit read only ID
Operating Frequency: 125kHz ± 6kHz
Communication protocol: EM4100
Recommended tag reader: RS 781-3061
Applications: Access Control, Anti-counterfeiting, Asset Tracking

Clear Disc (RS 843-0800)
Material: polyethylene and polyester
Dimensions: 20 x 0.6mm
Operating temperature range: -20 to +60°C

Epoxy Disc (RS 843-0806)
Material: Laminated Epoxy
Dimensions: 30 x 1mm, centre hole 3.2mm diameter
Operating temperature range: -40 to +85°C

Small Epoxy Disc (Rugged) (RS 843-0793)
Material: PPS and Epoxy
Dimensions: 12.4 x 2mm
Operating temperature range: -25 to +85°C

Nail (RS 843-0803)
May be hammered into wood
Material: polyamid with glass fibre
Dimensions: 35.5 x 4mm
Operating temperature range: -25 to +85°C

A range of low-cost RFID Reader modules and RFID Tags.