1. A warning system for a vehicle or the like comprising: means for receiving and sensing audio energy and for transducing such audio energy to output signals indicative of the frequencies, and of the amplitude of each frequency, of the audio energy sensed; means for converting output signals from said sensor means to discrete output signals representative of the frequencies of the audio energy received by said sensor means, said signal converting means being in output signal receiving contact with said sensor means; means for measuring the time during which signals are transmitted by said sensor means, and which, after one or more predetermined time period, transmits activating signals, said timer means being in output signal receiving contact with said sensor means; means for counting the discrete signals output by said signal converting means, said counter means being in discrete signal receiving contact with said converting means, and which, after making one or more predetermined count transmits an activating signal; and means for activating an alarm, said alarm activating means being in activating signal receiving contact with both said timer means and said counter means, whereby, when predetermined activating signals are received by said alarm activating means from both said timer means and said counter means said alarm activating means generates alarm activating signals.