Keri PKT-10X Proximity Key Ring Tag, 125 KHz Excitation/62.5 KHz Return, 1.51" Length x 1.15" Width x 0.155" Thick, Gray (Pack of 1) Smallest proximity key ring tag available Frequency: 125 KHz excitation/62.5 KHz return Robust and durable - washing machine tough Unique codes Lifetime warranty