Bedroom door can be opened with any card- how can I fix this or lock my window from outside?

I can lock my bedroom door all I want to but it can be opened by uninvited privacy invaders by anything from a credit card to a couple of pokemon cards. I went away for 3 days and came back to an extremely undesired situation which I won't go into here, but now I have to go away for a whole week. Is there a... show more I can lock my bedroom door all I want to but it can be opened by uninvited privacy invaders by anything from a credit card to a couple of pokemon cards. I went away for 3 days and came back to an extremely undesired situation which I won't go into here, but now I have to go away for a whole week. Is there a simple way to fix this without buying a lot of stuff from home depot? My door can't be jimmied open if I have something like a chair propped under the door knob- something I haven't had to do for several years but would gladly do now if I could then walk through my bedroom door and head off to the airport.

The room is on the first floor so I can then leave through the window which I do sometimes anyway just because it's much quieter than stirring the dog and leaving through the front if I need to head out after waking hours (no I'm not sneaking out or anything lol- I'm an adult). We've never had trouble with burglars or anything but the universe likes to send criminals to people who leave their front door unlocked for the first time in 40 years right? So I'd rather find a way of locking my window from the outside. Is there a simple lock I can buy from Lowes or even Walmart?
Update: forgot to mention I don't want to install a deadbolt on the door. Nothing that will affect the door, door frame, or wall
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