The Tail End Unit type TEU2 is situated at the boot end of the conveyor. Its sole purpose is to monitor the pre-start alarm tones on the V line from the controller at the drive head. If a valid pre-start alarm tone is received from the controller, the TEU2 will divide this tone frequency by eight and return the new, lower tone back to the controller via the S line. This process of modifying the pre-start tone and returning it to the controller allows the controller to verify that the pre-start alarm tone did not reach the boot end of the conveyor.