The folks that would go to those lengths can also hide them in their bomb or missile silo on their bug-out property. 
You know where thieves never think to look?
In the septic tank!
That’s where I hide all my shit!
Not exactly a hiding place, per se, but my brother showed me his alcove.
At the house-end of the garage, there was a 12-foot-deep loft space, where he kept some of his electronics hardware and some other stuff. On the back wall, there was a blackboard with a big cat-face-like chalk drawing accompanied with “Little know ye what evil lurks in the hearts of men”. By pulling out 3 nails in each side if the blackboard’s frame and lifting it off the vertical nails on the bottom, one exposed the hole he had cut in the wall leading into the attic.
The attic was filled with loose, fibrous insulation (not asbestos, AAUI) between the joists. Pushing it out of the way in the proper spot revealed a board over a hole he had cut in the ceiling. The door into the garage from the house opened on a landing that was one step below the kitchen, with stairs leading to the right, to the basement. The hole he had cut was above the slanted ceiling over the stairs.
The kitchen had a cabinet in the wall that went partway into the space above the stairs but a long way from using even a quarter of it. He had put boards to sit on and installed a fluorescent light in that small space, with bottles and a water jug full of the last batch of wine he had been fermenting in there several years before.
He also opened a space between the hall closet and master bedroom closet, but never did anything with it because it was just too impractical to use.
I’d hide money in the litter box as long as the thieves cleaned out.
My relative has a serious love affair with guns. What he has at this point are mostly handguns – a large (and extremely heavy) gun safe full of them.
He lives in a very temperate climate. When the stackable washer/dryer that lived within a main bathroom broke, he bought new units and put them on a covered porch.
He then converted the original location for the stackables (in that bathroom) into the spot for his gun safe. It was out in the open, so to speak.
Then he decided to travel the world.
He simple drywalled in the safe, and turned the residence over to a property management company to rent out while he travels.
Nobody’s ever thought to look for it, nor had reason to stumble upon it … apparently.
It sounds ‘too well hidden’ to be of any use, but you’d be surprised how quickly you could tear off the drywall if you were the owner and the need arose.
I think a towel rack pipe would be pretty good for cash. Roll it up and slide it in. Depends on the towel rack of course.
I have a situation where I want to hide a key outside of my elderly mothers house for 911 folks. I live far away, but I’m the first on her “I’ve fallen and can’t get up alert system” So I will need to explain where the key is. Bury it in one of the sprinkler valve boxes is my thought. I have a few ideas, but am thinking about burying it somewhere where I can easily explain where it is.
Her house is very secure, and I would rather not have the fire department breaking down her doors if for some reason she can’t answer and open a door. It’s already happened, but luckily, in that situation, my more local cousin has a key and got in. That was a broken hip.
Had another time when something apparently went wonky with her phone, and she did not answer for hours, and hours. My cousin was not available, and I was this >.< close to calling for a welfare check. Phone system came back up.
It’s very stressful. I need to fine a good, secure hiding place for a key for emergency services.
I would think that a key coded lock box like this one would be better, for a couple of reasons. 1) First responders aren’t going to want to go on a treasure hunt to find a key, nor may they have the time. 2) The code for the lockbox (mounted next to the door if possible)can be provided over the phone and then changed, rather than finding a new hiding place.
One option is a residential Knox Box, which apparently you purchase through the local fire department. Where my eighty-something parents live, the cost would be $170. So not cheap but perhaps cheaper than replacing the front door.
I know a smart-ass who, at a friend’s party, put some shrimp 
in a napkin into his pocket. He went into the bathroom, took the shower curtain rod down, put the shrimp inside the rod, then reassembled everything.
A cruel prank.
Those are notoriously easy to open. Lockpicking Lawyer has done a number of videos on them. If something like that were going to be used as a permanent solution, I’d suggest putting it on/near the back door so it can’t be seen from the road.
Another thought would be to get a smart lock. Depending on how comfortable both you and her are with the technology. Again, it could be put on a back door (even better if she doesn’t use it often) so it can’t be seen from the road. Then you can unlock the door with your phone to let in EMTs/neighbors in.
If she has a neighbor within a few houses one way or the other that she trusts, maybe they could hold a key. As long as you have their contact info, you could call them in an emergency to let the EMTs in (or just check on her).
In fact, it might not be the worst idea for you to get to know one of her neighbors. My next door neighbor called me once or twice while she was gone and her mom was at the house alone and needed help with something (semi-emergency type things, like needing help up some stairs and no one was going to be back for a few days).
That is just what I’ve been looking for! Thanks for the link.
I remember reading something like that. A couple was getting divorced, the person who was moving out put some tuna in a curtain rod. They were thrilled to hear from a friend that ex-spouse could never find the source of the smell. Even after they moved the smell somehow followed them to the new house.
No idea if the story is real, but it’s amusing.
I can be absent minded and would sometimes end up locked out. My former roommate used to live close so I could call him to bring over the spare key. He moved 40 miles away so I keep a spare key in a pretty unconvincing fake rock in the back yard next to the sliding glass door.
If you had no idea it was there you would never check as it is roughly the same color as all of the other rocks but now that I have told you any one of you dopers could probably get in …
I’ll bet the victim of that didn’t find it amusing.
As a young buck back in the day, whenever I took a road trip I would stash my weed in a fake can of Quaker State motor oil. The local head shop sold them. Looked absolutely real, and I made sure to use that same type of motor oil so as to have two or three real cans in the trunk along with the fake one.
Thanks for the replies about the key/lock box. I do have a cousin that doesn’t live to far away that has a key.
I have to think about this a little more…
It’s important to distinguish between hiding places that are inconvenient for burglars and hiding places that are inconvenient for you. You wouldn’t bother to sift through 5 gallons of dog food for some money, a burglar would take 5 seconds to dump it on the floor, and move on to the next likely spot.
Probably the best idea, once you’ve chosen a spot (mine will be inside the workings of a piano) is to email yourself the location(s) rathe than trust it to memory.
Pound a finishing nail into the trunk of a tree near your front door, hang your front door key from the nail. Paint the key so it matches the tree trunk and doesn’t reflect if someone happens to point a flashlight at it. This works very well especially if your yard has lots of trees and if you can remember which is the key tree.
Unless both parties have a habit of doing this sort of thing to each other, it’s isn’t funny, IMO, it’s just an asshole move.