a vmwi multisense detection device solves both the problem of long class vmwi signal retransmission delays and unreliable class vmwi signal transmission by simultaneously enabling both stutter dial tone detection and class vmwi signal detection . the multisense device samples the line each time the phone is placed on - hook or after the phone goes unanswered after a ring . if a valid class vmwi signal is detected before the scheduled dial tone test , the dial tone test will be canceled . if no class vmwi signal is detected , after a given amount of time , the vmwi device automatically enables stutter dial tone detection . the detection circuitry periodically polls for a preamble field of the class signal to determine whether a valid class signal is about to be transmitted . if the preamble indicates a class signal is being transmitted , the detection circuitry remains on and the class signal is received and processed . if no signal is detected during the time period for the preamble , the detection circuitry is shut off until the next polling period . this polling technique allows the vmwi detection device to operate only on batteries for long periods of time .