When you need to communicate with people who are at an outdoor location and you can’t run wires to that location, an outdoor wireless intercom is the solution. These outside wireless intercoms communicate to an inside station or portable handheld two way radio via radio waves.
There are several varieties of these outdoor wireless intercoms available. You can get heavy duty, tamper resistant devices that communicate over long range, or lighter duty devices that communicate a few hundred feet. Some devices communicate using a proprietary method that only allows devices from the same manufacturer to talk to each other, while others are more open and allow mixing devices from different manufacturers. If you have existing two way radios you use, you can also get outdoor wireless intercoms that talk to them.
One system available is the WireFree Outdoor 900MHz Intercom. This is a proprietary system that will only communicate with other devices in the WireFree product line. It has a range of up to 1000 feet, but with obstructions in between is more likely to be a few hundred feet. These outdoor intercoms communicate with other WireFree outdoor intercoms or with the WireFree Portable 900MHz Wireless Intercom for inside use. These outdoor intercoms work in walkie talkie fashion where a button push is required to talk.
If your outdoor wireless intercom application is taking calls from visitors at your front door or security gate, then a wireless doorbell intercom is what you need. The WireFree Wireless 900MHz Doorbell and Intercom works with the entire WireFree product line. When visitors arrive at the door or gate they press the button on the outdoor wireless intercom and it sounds a doorbell tone on the inside and outside units. The person on the inside presses a button to talk while the person outside can talk hands free. This unit has the same range of a few hundred feet as the other WireFree products.
If you need an outdoor wireless intercom that communicates over long distances, then a wireless call box like the MURS Callbox XT Outdoor Intercom is needed. These devices use UHF and VHF frequencies to communicate over long range. Some of the wireless frequencies require an FCC License, but the MURS Radio frequencies are unlicensed and very lightly used. These callboxes communicate with two way radios or base station intercoms.
If your application requires unlocking a gate or door from a remote location, then 
the MURS Callbox XT Outdoor Intercom with Gate Relay is what you need. This call box has a relay that can be controlled by pressing a button on a wireless intercom like the MURS Commercial Intercom or any two way radio with the 2-tone encode feature.
These outdoor wireless call boxes are also built for more commercial or industrial environments. The XT version of the call box is also vandal-resistant so it is good for use in public locations.
Choosing the right wireless outdoor intercom for you depends on your application and your budget, but you can usually find one that will work for you.