Netherlands-based wireless innovation company Waleli has developed a GSM doorbell. It allows people to answer the door, talk to visitors and even open the door, whether they are at home or not, via telephone over the GSM network.

When the bell is pushed, the GSM doorbell calls the occupant who can then to speak to the visitor. By entering a pincode on their mobile phone, the occupant is able to open the door.

Source

Building Sustainable Design