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.