If you do not have an entrance door to your garage either to the interior of your house or the exterior there should be a key based garage door release on the outside of your garage.
Pry garage door open.
Garage door locked from the outside.
These openers use a threaded rod to push and pull a trolley that lifts and lowers your garage door with ease.
In order to do it properly and safely you can follow these steps to open your garage door with a broken spring.
If the power comes back on the opener might attempt to open the door while it is disengaged which can make it harder to reconnect.
On either side of the garage door place two 6 foot ladders.
Unplug the automatic door opener.
Ever forget your keys to the house or even lost your garage door remote.
Unplugging the garage door opener before you try to manually open or reconnect your garage door will keep you safe.
For a garage door opener that is quieter than your typical chain drive model consider the convenience of a screw drive garage door opener.
You would obviously need the key for this but it would release the garage door without resorting to prying it with a hanger or another similar hack.
When you open a garage door by hand make sure to stay safe.
Get two crowbars or pry.