doors
A rarely used exterior door mortise and tenon does not align. Although the door closes, the doorknob's tenon does not enter its mortise. The same is true for the deadbolt. The tenons shown in the photo is low relative to the mortise.
What options are there to enable the door to lock?
I am considering a new slab door, however, I am hoping for a quicker, cost effective solution.
You don't necessarily need an electronic lock - you just need a lock that is always locked from the outside and yet allows exit from the inside. Something commercial in nature is probably in order. You probably won't find this at a home supply store, however. You likely will need to consult a locksmith.
CORRECTION
Link to Home Depot collection of storeroom locks.
You can find them at Home Depot.
Thanks to RSMoser for the proper name!
I'd look at hinge stops, and use them in pairs (or even triples). They apply a large force to the hinge screws and the door skin, so using multiples distributes the load.
For reference only.
If your doors are very heavy, consider a closer as recommended by Ed Beal.
Best Answer
Easy enough to move the strike plates to algn. You may have to increase the size of the mortise with a wood chisel. Fill the old holes using toothpicks or a small dowel and wood glue. Then reset the strike plates.
It's about as cost effective as you can get.
Another option I've used is to install a hinge spacer on the bottom hinge to raise the door up slightly. You can get them at most home stores. Obviously, you need enough play around the door to accomodate the movement.