InterTalk&reg; FM 132 4 channel 4 units TRADITIONAL FM Wireless Home & Office Power-line Intercom system for 110 Volts Expandable. You can buy additional sets & add on to the system. (see bullet pt # 3 in Knowldege Base for guideline) Digital Control function Panel. No intermittence contact problem Security- All conversation travel from outlets to outlets within the same power meter of the building. No bugging and no eavesdropping. No Crossing from one power meter to another. Multi-channel with slide switch for designated station setting for user to pick a good channel for monitoring 12 months factory warranty. Just keep your receipt | System Requirement: The system must be used from within ONE Power Meter. 2 or 3 pronged 110 Volts in-wall AC outlets || BUYING GUIDE: * Upgrade you existing 2 pronged intercom to this 4 Channels Intercom. * If your existing intercom is 2 pronged, this is your exact REPLACEMENT. You can simply plug them into the same exact outlets. * If you have a mix of 2 pronged & 3 pronged oulets in your house, You should buy this model. * If ANY of the 3 pronged outlets in your house is not grounded, You should buy this model. * The difference between a 2 pronged & a 3 pronged intercom is Phase Bridging. In a word, with a 3 pronged system, you don't have to search for an outlet that is in the same phase. The time needed to set up a 2 pronged system ranges from 10 to 30 minutes depends on the number of units and the size of the building. An "2 Pronged Setup & Troubleshooting Guide" is included in the box. ||| KNOWLEDGE BASE: * The term "wireless" is a branding employed by those BIG retailers from over 20 years ago. The official product name is Power-line Intercom System. * Simple power-line communication. NO Radio Wave. Therefore NO transmission nor receiving process. * There are no fix rules on how to utilize the channels. It can be used as all paging, monitoring or unit to unit per designated channel communicating. Combinations can be 2 sets of 3 channel twin set & make it six units, or one twin units 4 channel sets. Some users would believe the number of channels = to the number of units. This is not exactly true. * Power-line Intercom systems communicate via the power-line of the house; therefore it has further distance further distance than a Radiowave Frequency intercom, free from building material obstruction like concrete, and it has no EMF danger. * Since voice travel via the power-line, all 2 pronged units must be plug into the same phase of the AC supply to communicate.If the system is plugged on to same phase of the wire, they are NOT on the same line, they will NOT communicate * Power-line Intercom System uses the AC power line as the medium. It is subject to any interference already existed in the power-line, Just like your AC AM Radio. There is NO defectiveness with the system. * Statics & noises interferences) were feed into power-line by bad appliances with characteristics of hums, buzz, sizzle or roar punctuated by pops & crackles. About 8 to 10% of the households are affected by Interference. Power-line intercoms rely on power-lines for communication. Interference affects 1 maybe 2 channels on the whole spectrum of the bandwidth. To meet the challenges, multi-channel intercom was created as a solution for users to pick a clean channel for the monitoring purpose. * Dual Phase AC wiring is defined as One 220 volts service drop from the utility company coming in to the building. The 220 volts is divided into two phases of 110 volts each with half the building wired on one phase and half on the other to even out the load. In an optimal scenario, the upper outlet is phase one & the lower outlet is phase two. Dual Phase wiring affects all building in North America. * Power meter: In general utilities supply & billing, one household should have only one power-meter. Multiple power meters situation is common in some commercial units, when the tenant rents 2 units & joint them as one. In a residential situation, multiple power meters are possible with duplex. All power-line Intercoms transmit & receive within one power meter. This is a major security feature.