A pictorial and a video demonstrates how to build an invisible switch into a PC. A schematic is shown how to apply this technique for cars.
Step 1: How to make an invisible switch in a PC step 1
The first picture shows the reed switch which we will use. It's a glass tube with two contacts which are pulled towards each other making contact when a magnetic field is present. You can reed(read ;-) ) more details on wikipedia. http://en.wikipedia.org/wiki/Reed_switch
For the PC we'll use a read switch with a make contact.
The first step is to remove both side pannels from the pc housing by unscrewing the bolts shown in the picture. After that the front panel can be removed by pushing the front panel retainers together with your fingers to unlock them.
Step 2: How to make an invisible switch in a PC step 2
Now we can twist our read switch to the wires. Once the switch is twisted on, we can tape it to the front panel using some quality tape, so it won't let go. Mount the reed switch on a place where the front panel is not very thick, otherwise we may not be able to operate the switch.