["For the car, if my keys were locked in the car I'd ask the cops to slim-jim it for me."]

The cops may want proof that you own the car BEFORE they slim-jim it for you.
My 2 cents
Adventureboy

Spare key in my wallet and one hidden on the vehicle. The neighbours have a spare key to my house and kids have a hidden key outside.

If you are ever in a remote location and need to get through a gate in an emergency just look under the closest rock or behind the nearest tree, lots of hidden keys in the bush.

Almost every remote camp has a hidden key, check on top of the door frame and in the outhouse first.

Mike

I use the one way screws on my plate...the type that can't be unscrewed without a LOT of hassle and time spent. A thief would simply go on to another car after seeing those.

Would a metal detector help?

"So: where's a good place to hide a key/magnetic box that's not readily found by vandals on a fishing expedition?"

The same as when on a car camping trip: dump the box and put the key on a cord around your neck.

Sue

I used to keep a car key wired to the frame of my old car. Almost impossible to spot or feel.

For the house, there's a key inside a film can and buried about 4" deep by a landmark. It would take a messy minute or two to dig it up.

They have ways of finding out. :->

Good idea, but not so good in winter in Canada. First you would have to dig through the snow, then through the ground frozen like concrete.

The film canister hidden above ground would work better here.

Mike

I carry a spare house and car key, and have the garage door opener in the car that will let me in the house. As a backup, a friend has a spare house key. Worst comes to worst I could break into the house.

The car, other than the spare key, is more of a problem. The car has one of those *&^&^ computer chips, so the car won't work without the special key. This will be the last car I own that has that, unless I have no other choice. Ideally I'd have push button start and keyless entry. This is 2009, why should I need a metal key to operate my car? That's like 11th century technology.

I like your thinking about keyless entry and starting Tom, but how well would it work in the cold or with minimal battery power?

Mike