Yeah, if I post my favorite hiding spot it’s no longer a secret.
When we used to take Girl Guides camping, there was a site, that while in the countryside, was not all that far from a council estate. The hut where they stored equipment was broken into several times so they got together to make it as secure as possible.
It is a brick-built shed basically, and the windows were the first consideration. They were all bricked up, leaving only a transom window at the top, about 30 centimetres high. When the hut was empty, they were secured by steel plates on the outside, held in place by wingnuts on the inside.
The main double doors were clad in steel, which extended over the wooden frame so that not even the hinges were vulnerable.
To get in, we were given a key with a long shank. The back door, again clad in steel, had a small keyhole but the actual lock was a good 15 centimetres inside so that superglue wouldn’t work. (yes that was tried).
Turning the key allowed a small hatch to open and you could put your arm through to swing a substantial cross-bar in the inside out of its clips, which then allowed the door to open outwards.
The roof was still vulnerable and the defences mainly focussed on preventing anyone from climbing up. Barbed wire and special paint was part of it.
Of course, it is not a vault. The defences are against bored teenagers, not professional crooks. Nothing in the building had much value - there is no great market for secondhand tents or well-used cooking implements. After all that it was just the obscene graffiti we had to deal with.
And that’s the thing. In general, most of us that are securing our houses or cars are just trying to get the would-be thief to keep moving, not stop a targeted attack. That’s why leaving a TV on or having a barking dog will send a burglar to the neighbor’s house.
I don’t have anything hidden right now. I mean, I have an envelope with about a grand or two in it, but it’s just in my closet, no need to look for it, just turn your head.
Other than that, I honestly can’t think of any valuables or keys or anything like that hidden away. Whatever there’s worth stealing is in plain sight. Have at it.
I used to have a hidden house key and hidden car key back in the day. To find the hidden house key, you first had to find the hidden garage key in the electrical meter. Then, once you figured out it’s the garage key and not a front or side door house key, you have to find the house key semi-hidden in the garage (it wasn’t even in a drawer – just tucked away on a nail by the tracks of the garage door.) If you were unlucky, you found one of the other keys in the garage for something else. (There were some keys in there I had long forgotten which lock they went with – probably from old locks, too. They weren’t purposeful red herrings – there just were a lot of keys around for some reason.)
My car had a similar, but easier due to search space, two-part solution to finding the car key. (This was, of course, back when cars had keys and, even more, the ignition and door key was different than the trunk key.) I’d keep a spare trunk key screwed in behind one of the plates, and then in the trunk, somewhere was tucked away the door/ignition key. (I think those were the same key, right? I can’t remember it was so long ago. Or was there a separate door key? I just remember the trunk key being different than the door key, and my memory is only needing to keep two, not three, keys around, so the door key must have been the same as the ignition, unless my memory is faulty, which it may be. Hmmm…maybe it was a three-keyed set-up now that I think about it. That actually makes a little more sense. So the door key would let you access the interioir where, presumably, your ignition key is – which was the whole point of hiding these keys in the first place, in case you lock your keys in the car.)
I only ever had dual key cars. My recollection is that generally the main key opened the door and started the car (made sense, you didn’t have to swap). The second key in my recollection only locked the glove box, but possibly it did the trunk also. I was told the theory was that then the valet couldn’t get at all the valuable stuff you kept in the glove box (and I suppose the same would hold true for the trunk, before inside trunk releases became common).
OK, then my original thought was actually the correct one, and I should learn not to second-guess myself. 
During my first marriage, I socked away a couple thousand dollars a bit at a time. My “bank” was a tampon box kept under the bathroom sink.
That’s what they all say, then the kids end up finding thousands of dollars in all kinds of bizarre places when they’re cleaning out the house.
Sure. But it’ll be the previous house owner’s. I just don’t hide things.
Pretty much that.
All the locks and barbed wire and chains and so on just keep honest people honest.
A professional thief might be slowed down by all that stuff, but that’s about it.
I keep my bike safe when I lock it up on a bike rack in NYC by putting it next to a really expensive bike. 
My dad used to keep his loaded .32 and my mom’s jewelry in the drop ceiling in one of the bedrooms. Yeah, that was pretty easy to figure out as kids, and I can’t imagine any burglar worth their salt not thinking of looking in the drop ceiling.
I think it just depends on the thief. I remember an article I read years ago where they interviewed a bunch of ‘reformed’ thieves. Asking them what they did, how they broke in, what they looked for etc. One of the questions they asked them was what would prevent them from entering. They all gave the interviewer different answers with respect to things like ‘ADT’ signs or a car in the driveway or a TV being on, but every single one of them said that if they heard a dog, it wasn’t worth the trouble. Little dog, big dog, doesn’t matter, it’s not about getting attacked, it’s that the barking will inevitably cause someone to look over in the direction of the house and possible notice there’s something wrong.
Maybe quickly sticking your head up there. But I’m sure I’m not the only one who’s put things above drop ceilings. If it’s something ‘short’, you really can’t see it from way across the room. That is, if you put a gun up there and I stick my head up (where it’s dark, dusty and may have pipes/ducts in the way) 15 feet away, I probably won’t notice it. And even if you’re robbing the house and aren’t concerned about the damage, knocking out every panel seems time consuming.
I can’t imagine any professional burglar not at least taking a peek inside a dropped ceiling.
Law enforcement, on the other hand. . .
Canadian police investigating the serial killers Paul Bernardo and Karla Homolka failed to find videotapes they’d made of some of their murders stashed in the dropped ceiling of their home.
The prosecutors, unaware of the evidence that Homolka was an active, willing and even enthusiastic participant in the murders, gave Homolka a deal to testify against Bernardo.
He got a life sentence, and will never, ever get out of prison.
She’s walking around free today, and has been since 2005.
The videotapes were discovered (not by law enforcement, by Paul Bernardo’s lawyer, who sat on them for a long time), but only after the deals were made.