Linksys routers have been very versatile at doing many things besides just routing your internet. In this example, Sunlight Labs used an old Linksys WRT54GL router and Arduino relay interface to create a cheap automated door opener.
The Linksys WRT54GL’s firmware was replaced with OpenWrt, an open-source linux firmware that can be used on the Linksys router. The beauty of this hack is that the hackers(Sunlight Labs) used DMZ LED pin as an output to control the relay which can open the door. I think this can be used as an example for others to hack their own Linksys routers as the DMZ LED pin is one of the GPIOs.
Also, I am sure you can hack it a bit further to make door opening possible through an iPhone/Android app. That’d be a lot of fun, authenticating yourself with a cellphone to get into the office.
Really, there are many cheap, old Linksys routers you can buy and this proves to be an example of good use of both linux and old routers.
With the firmware installed, I was able to SSH into the router and perform some simple manipulations of the system’s GPIOs — General Purpose Input/Outputs. These connect to things like the system’s LEDs and switches, and can be controlled in software. I selected a GPIO that didn’t seem to be used by OpenWRT — it illuminates the “DMZ” LED on the front panel — and wrote a very simple script to control it. I could now flip a tiny light on and off from a network connection. The hard part was over.