Honda's have been doing that for as long as I can remember. You can hold the
driver's outside door handle up and push the lock button, then close the
door as well.

GM has recently made the locks not work right away either. You push the lock
button on the door and the doors won't lock right away, takes a minute. Not
sure how well that works for not locking you out.

Steve

Most auto door locks I've seen in recent years have had such a
mechanism, on the driver's door at least.

I doubt it can be retrofitted on a mechanical lock. Some electrical
locking systems will unlock the door immediately if you try to lock the
door while it's open and the key is still in the ignition; if you really
want to add this sort of feature to your car, that's what I'd investigate.

Might be easier and cheaper to keep a spare key in your wallet, unless
you're in the habit of locking both keys AND wallet in car. Downside is
that if you lose the wallet someone now has a key to your car and a good
guess about where it will be parked. So a better low-cost answer might
be to leave the spare key someplace else where you can get to it (ask a
friend to hold it for you, for example).

This is a new and special feature to you...?

My 1962 Dodge, just like all its brethren, has the same feature. So did my
1965 Valiant. Amusingly enough, in 1971 Chrysler Corp. _deleted_ this
feature from all their cars, and marketed the change as "Keyless locking";
i.e., you had only to push the button down and close the door, and it'd be
locked. Apparently you can't please everyone.