S J Security Systems Pvt. Ltd. Offers Audio Door Phones with Electret Transmitter. It is flexible and can be adapted to the architecture of the building. These are used in all varieties of door stations, from single-row systems to multi- functional systems. Made of ABS-plastics, S J Security Systems Pvt. Ltd. Offered Audio Door Phones with Electret Transmitter is available in four attractive colours. The green operating indicator is used for speaking and door opening. The dimension of the product is width 84mm; height 220mm; and depth 60mm.