| 摘要 |
A vehicle security system comprises a control unit 10 arranged to produce a coded electrical signal, a warning siren unit 12 arranged to receive the coded signal and, when the system is in an armed state, to produce a warning if it detects that it is not receiving the coded signal. The coded signal comprises a rolling series of codes, each comprising a plurality of bits separated by inter-bit intervals of substantially no current. The inter-bit intervals are substantially longer than the bits, and are the same length as intervals between codes. This arrangement reduces the current needed for transmitting the coded signal and for rolling it, and makes unauthorized recording of the code more difficult. |
