SHARED BY ONE OF OUR NEIGHBOURS: Last March I had my garage broken into (in the alley west of Hamilton St). A bunch of tools were stolen. Access was gained with some kind of coat hanger/hook forced through the weather seal at the top of the door. They were able to catch the red pull line that releases the door from the chain, then lift the door by hand.
There are a lot of youtube videos on how to prevent this. Easiest is just to shorten the pull string (or remove it altogether) and zip-tie the little lever so it can't be pulled without cutting the zip-tie.
Here is a quick (3 minute) video that explains more: