Need help from someone who knows a little chemisty

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I'll explain the situation first. My girlfriend lives near a rough bar and every night people urinate outside her door. She's tried putting CCTV signs on the door which has made no difference... so I had an idea.

I remembered the alkali metals experiments from school and thought I could give them a fright by leaving some lithium/sodium/potassium in a glass of mineral oil. When the drunk steps up to urinate I doubt he can resist aiming for the glass and subsequently he should receive a shock and learn his lesson. This may be p***ing in the wind a little (excuse the pun) as it is unlikely to be just the one offender however I feel it would be worth teaching at least one person a lesson.

My question now is... can I obtain a highly reactive alkali metal legally in the UK, and if so which one would be best suited for maximum impact without being excessively dangerous? If they are highly controlled, as I gather they are, how difficult/dangerous is it to produce a sufficient amount from readily available chemicals?

Honestly? I think it's a terrible idea. There are all kinds of issues around whether or not it's legal, and safe, and who's liable. Bear in mind it's possible for those metals to start fires - not what you want near a door, whether wood, uPVC or otherwise.

You'd be better setting up a motion-activated light, and possibly a motion-activated webcam. Your girlfriend could then turn the footage over to the police, if the light doesn't scare them off. These people are committing an offence, and it would be a lot more effective for them to get ASBOs than for you to start messing around with reactive metals.

If you do decide to go ahead with this, under no circumstances should you use rubidium or caesium (assuming you can even get hold of them). They are extremely dangerous and react explosively with water. (And I really do mean explosively - a couple of grammes of rubidium will go off like a small bomb.) We're talking the sort of reaction which could cause injury to the drunk (if nothing else, from flying glass), and would probably attract the attention of the police.

I really, really think you should reconsider this.

yeah...and sodium bursts into flames on contact with the air. The glass could just fall the wrong way, and set your flat ablaze....

You'd probably do better to contact the police, and have them cruise by around closing time. I'm sure that public urination is a crime, even in the UK...

Or maybe some sort of alarm...

To add to the problems, the urine stream has been shown to be too divided to be an effective conductor of electricity. So even if you found a power source and created a live wire for the drunks to pee on, they'd still be safe.

Drunk and disorderly, and urinating in public are misdemeanors. Setting up your property or someone else's as a potentially
lethal trap is a felony. Think about the consequences if someone gets hurt.

The sodium idea is a bad one, if you mix sodium with water you can get a very loud bang which will wake the dead, attract the police, smash glass objects and get you into a world of trouble.

If you put up flood lights and make the area brightly lit up then the drunks may be less likely to wee on your property.

It might be worth planting a nice looking but sharp and spiky plant in the front garden. That might keep the drunks at bay. I imagine that if you were about to go for a pee in the dark, stepping towards a sharp spiky plant might make you reconsider and then go somewhere else.

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Diagnosed under the DSM5 rules with autism spectrum disorder, under DSM4 psychologist said would have been AS (299.80) but I suspect that I am somewhere between 299.80 and 299.00 (Autism) under DSM4.

It wouldnt surprise me if its the same person/people each time.

That or there is something that is particularly attractive about pissing on her door. Maybe its in shadow?

If I wanted revenge I would do the glass/container trick, but have it almost full of water, with two electrodes that complete a circuit when "water" is added. This opens a valve overhead, releasing piss onto them.

You could even set it up with a counterweight. Nix the electrical connections.

put some strong lights, I mean, STRONG ones, that'll do.

I could tell you where and how with the alkali metals, but its too dangerous and you will get in too much trouble,

How about something a little less harmful yet mischievous.

The psychology of drunk guys wanting to urinate on an object can be put to good use.

I was thinking about a spring loaded cup with a sugar cube "fuse". When the urine dissolves the sugar cube, the spring platform launches the cup onto the urinator. This device could be called - "sweet reprisal"

A suitable spring platform may be a mousetrap. The cup has to be paper or plastic with a hole about 2cm up, so as to collect some payload pre-launching. When the level gets up, the overflow dribbles to the sugar cube and the cup is launched. The mouse trap levers may have to be bent to accommodate a sugar cube, a straw may be needed to transport the liquid from the cup to the sugar cube and some cutting of the mouse trap may be required to help disguise it. Also, a fast food wrapper can provide further camouflage. Use water in development / testing for obvious reasons. If you want to really mess with them, set the trap up with a bit urine coloured liquid in it to start with so they think they got a dose of someone else's..

Another possibility could employ a U shaped bracket and a rubber band across the tops of the U. A shortened plastic spoon is wound into the rubber band so that it spins wildly when let go. The spoon is positioned through the rubber band to nearly touch the bottom of the U, where a sugar cube can be used to chock it. The device is put into a cup. The spoon spins wildly and splashes liquids everywhere when released, so would not be as directional as the mouse trap version, but the sudden rattling sound may provoke a funny dance.

I will stop at two designs, engineering solutions to daily problems come to easily to me..

I normally design more useful things off the top of my head as I am an inventor / scientist, but this one just seemed too amusing.

Or you could just put sheet metal on the side of the building where they are going and then hook it up to a fence charger. That should do the trick.

Mythbusters did a show where they seemingly disproved that peeing on the third rail was fatal, but I don't believe it. I say lets test it on your drunks.

Of course, if you just installed an outdoor urinal, that would solve the problem too.

This reminded me of one of those Belgian statues that pee.
And I imagined making one out of plastic with a water pump that is activated by
when two wires get wet from being peed on by a drunk. (Typical wet sensor)
And it's up high above out of reach and it pees on the peeing drunk with just water.
And the light going on at the same time and also making a funny noise.

But it should know the difference between pee and rain, methinks.
And somehow not be obvious except during pee time.

Alkali metals are a bad idea. The only ones which one could use for such a scheme would be lithium, sodium or potassium. Rubidium and caesium are so reactive that they will explode on contact with air (and given their high atomic mass, they actually have much less energy per gram, making any explosions they produce much less energetic than their higher homologs), making them pretty impractical for just about everything. As for francium, which I just thought I'd mention for completeness sake, nobody could use that even if they possessed all the money on Earth. The most stable isotope of francium has a half-life of 22 minutes, which is a little short, and there has never been assembled more than a few hundred thousand atoms of it at a time. In addition, every second it releases ~600 times as much energy through radioactive decay as is released through its reaction with water, making reacting it with water somewhat redundant. If you could get a visible amount of it, it would probably look a lot like the surface of the sun, and after you are consumed in a radioactive fireball the resulting effect on the neighbourhood would make Chernobyl look like an environmentalist's dream.

So, to the serious contenders, sodium, lithium and potassium. Lithium has the highest energy of all the alkali metals, both on a per mole basis and in terms of mass. However, it is also the slowest reacting of them - a sample of lithium immersed in water will only slowly produce bubbles of hydrogen and will typically not ignite. As such, it probably isn't all that practical if one desires a rapid, water induced explosion. That leaves sodium and potassium. Both will explode on contact with water; however in the case of sodium this really depends on the amount used - smaller amounts will merely ignite, and really tiny amounts will only manage to produce copious amounts of hydrogen. Potassium is much more treacherous. So anyway, either of these will produce a fairly dangerous explosion. However, it is not really the explosions themselves that make these dangerous. Rather, it is the products formed by the reactions that lead to the greatest possibility of injury. Reaction of the metals with air will produce the metal oxides, and reaction of the metals with water with the metals will produce the metal hydroxides. These are highly alkaline and consequently highly corrosive, and quite adept at dissolving human flesh (and they are much more corrosive at several hundred degrees, as is the case when they are produced in an alkali metal explosion). And these, lovely corrosive compounds will be splattered all about the place by the explosion, which means there's a good chance that you would render said drunkards permanently incapable of having children, which while perhaps improving the gene pool slightly would also render you in some degree of legal trouble.

If you insist on doing something chemical, it would be much safer to do something involving the production of an irritant gas. For instance, a dry mixture of sodium bisulphate (or any other solid acid) and sodium sulphite, will release SO2 on addition of water:
2NaHSO4 + Na2SO3 -> 2Na2SO4 + 2SO2

Sulphur dioxide, as anybody who has ever set sulphur on fire will know, is a very unpleasant gas to be around. Though not overly dangerous (in part because its properties make it very unlikely anybody will hang around to breathe a dangerous amount in) it is very irritating, typically leading to coughing fits so long as one remains in contact with the gas. If you're not intending to permanently maim the person, then SO2 is definitely preferable to a setup which involves flaming sodium being blown through the air.