The SENTRY Code Hopping transmitters are secure products utilizing KEELOQ encryption, operating in the 433MHz range. These are standard encrypted remote controls that generate unique encrypted transmissions with each keypress, in either one, three or four button option. Employing secure KEELOQ encryption, they provide the ultimate level of security- they are exceptionally resistant to code grabbing. The encryption is also sufficiently large to render an attack very time consuming (8 years). Each transmitter is unique and contains a unique serial number that is never duplicated. KEELOQ is a trademark of Microchip Technology Inc.