You can use this to copy a cylinder lock key within minutes. Especially great if you have a key that says 'do not copy' on it. You will need:
Access to the key (for a few seconds)
A drinks can or other thin metal
Ruler or other hard blunt edge
I have copied a master key for an entire office block doing this and it worked fine.... I have also copied a Yale lock key for a lock which I have been having trouble picking.
Step 1: Copy the key - quick!
Get a copy of the key using either:
Scanner - easiest
Camera - you must have a scale present in the picture (ruler etc)
Impression in bluetak or clay, then scan it or photocopy it. I personally would try and highlight the impression with tipex or something first to ensure a good print.
Print 2 copies of it in the correct scale so that you have two 1:1 copies of the key
Now roughly cut the copies out. Don't worry about cutting each tooth properly, just leave excess paper around it all.