Linear actuators have the power to be critter crushers.
Don't have to use one, here is my solution to that problem.
(I know it is dirty, but won't clean it, have to smell as much of my cat as possible or others will come in, and the lock is not done yet, still struggeling with the rfid range being about 5mm
That is strong enough to hold the cats out, and at the same time not strong or big enough to hurt anyone.
My program is keeping an eye on the magnet holding the door closed at the same time, so 5 seconds after unlocking, it will wait for the door to close, and if it have been closed for 500 ms (not just a fast sving-by) it will turn the servo to lock position again.
This is only keeping other cats out, which is good enough for me, but two way can be made too, just cut away a bit of the plastic at the bottom, and the servo is then thin enough to go underneath the swinging door and reach the arm up on the outside of it, just make sure to somehow waterproof it then.