I don't have a key for my front door (that atomatically locks) so I want to know how to keep it open without anyone noticing.
Get a duplicate key or change the lock so that you have a key.
I DO NOT recomend trying to bypass the security, but for a short period, take a piece of duct tape and put it running up and down on the edge of the door so that it holds in the striker. Check for clearence by closing the door (while inside) and making sure that the tape doesn't rub, or else it will peel off, and you're stuck.
Good Luck !!
Its extremely unsafe but you can test wedging paper or a piece of cardboard between where the lock goes in (socket) and the actual door part that goes in (plug).
Test this with someone inside so you dont lock yourself out..also this is unsafe because if you ever get robbed you'll feel dumb for not having replaced the lock.
Please do not take the chance that someone may hurt you because they can get inside you house. If possible call a friend and ask them to buy a lock and and you do not leave the house until you install a new one.
hmmm put a small object between the small gap (this might screw up your lock btw im just guessin XD)
do you have a window you can go throw.
or can you replace your door knob and get a key?