The security door at the front of [Oliver's] building uses an intercom system to let in guests remotely. Each unit has an intercom handset with a button that unlocks the door. [Oliver] wanted a way to enter without carrying any extra items so he built a system to unlock the door with his cell phone.
He patched into the intercom and attached a GSM module. The module runs python so he wrote a script that will monitor the entryway buzzer, then wait for an approved cell phone connection to unlock it. He went through a couple of different iterations for the final project. The first attempt used XBee modules to communicate between the intercom handset and the GSM module. For the final version, he snaked cable through his wall using rare-earth magnets (creative!) in order to forgo the use of a battery in the handset.
Who doesn’t carry a cell phone with them? Because of this, the use of GSM modules in automation is a trend we think will continue to gain popularity.