Sleeping/Narcotic Gas Alarm

You are right to be worried. Here's an article in a popular British Newspaper: http://www.dailymail.co.uk/news/article-1302917/Gassed-beds-Riviera-robbers-Terrifying-ordeal-British-tourists-falling-victim-Mediterranean-gang-crimewave.html It is in fact very common. The gas they use is nitrous oxide and contrary to what a previous poster has said, there are alarms which detect such gasses as these alarms are available to dentists to prevent accidents from leaks. I have been gassed on an overnight train going through France and a couple which I am friends with were gassed in their caravan in France. They slept on top of their money and the criminals actually moved their bodies to get to it. They took everything including clothes. It's really not nice to dismiss these reports as myths when you people really have no idea what is going on out there. Where I live in Scandinavia one of the biggest retailers actually sells narcotic gas alarms. How effective they are I can't say but I don't think I would be relying on that alone if I was worried. And to the poster who said what would you do if someone did come in and you were awake as though there is nothing you can do..... You can call the police for a start. I know someone who hunts deer and camps in a caravan. He has a narcotic alarm so I don't think much good would happen to anyone who decided to gas his caravan.

Quite apart from the other answers, what would you even do if your detector goes off?
Are you also going to carry a gas mask and full protective gear (gas can affect you through the skin, at least some of them) and are you trained to put it on under stress quick enough to be effective (likely seconds)?
And then, if a group of criminals were expert enough, determined enough, and resource rich enough to have access to sleeping agents and the means to disperse them AND knew how to use them, do you really think they'd not have other means to subdue those who fail to be knocked out by that gas?
Things like knives, silenced guns, clubs, lethal injections? Things that will surely kill you because now you've actually seen them and could be a witness against them...

It not only just doesn't happen so there's no need to worry about it happening, it also were it to happen would only make matters worse for yourself if you didn't succumb to the gas.

The reason you're finding that they only have them in Europe is gassing is not a common problem in other parts of the world. (Honestly, it's not that common in Europe either). In most dodgy parts of the world, criminals will force their way in, jimmy the locks, or just wait outside your door. Slip something in your drink, or even just blow scopolamine in your face (the last one terrifies me). You can worry about these things, or not. But traveling is very similar to investing, know your risk going in and determine your maximum loss.

With that said, the string of gassings appear to be in rich resort towns, targeting villas, etc. They appear to pick the places by targeting expensive rental cars, located in front of nice rental houses. If you're going budget, you likely won't encounter these things.

Still not convinced? Grab the gas detector. Sometimes peace of mind is worth a couple hundred bucks. But the gas detectors are tricky, since they detect different gasses, and you need to predict what type of gas they might use. Most common in the EU is Nitrous Oxide, and most detectors being sold are meant to work inline, and are not effective at detecting ambient levels like a smoke detector. By the time it detects ambient levels, you'll likely be knocked out with the alarm going off, and what good is an alarm if you can't move?

But once again, these things are extremely rare. I'm on the road almost 40 weeks a year and have never come across this. Most of my friends living in dodgy parts of the world (Somalia and Cambodia come to mind), have been robbed. But it's always blunt gun or knife point. All you can do is act smart, don't flaunt your money, and make safe and reasonable decisions.

All the best and have a safe trip, the world is much scarier before you experience it.

Seriously, this is not a problem.

Why ? The brother of my former girlfriend was an anesthesiologist. I was interested if it is possible to have something for sleeping (I am seasick) and I got a longer speech about anesthetics. Concerning gases: If you are not an expert, trying to gas someone does either nothing, alert you immediately or kill you.

Mind you, this were experts:

http://en.wikipedia.org/wiki/Moscow_theater_hostage_crisis

and it killed more hostages than bullets and it did not knock out all terrorists.
Robbers do not gas someone, they are relying on brute force (smashing the door). Thieves are not stupid enough to risk killing the victim. Buying a gas detector is lost money. And really, do you expect that criminals carry along flasks of sleeping gas which are not even guaranteed to work ?

This does not mean that criminals cannot knock out victims, but they are either spiking your food with drugs or using needles, in both cases they need contact to you or to your food. The chloroform or ether rag from the "damsel in distress" movies are mostly fiction, too. They may work, but they are dangerous (killing you) and unpredictable (suffocation, not working at all). Another option is tasering.

If criminals do not use violence, they simply rely on stealthiness. Once inside, they plunder noiselessly and if they are afraid that you wake up, they are now in vicinity if they are really intend to knock you out.

EDIT: More info in this thread: I also recommend the calculations how much gas of different sorts are needed to flood a room on page two.

Royal College of Anaesthetists

Despite the increasing numbers of reports of people being gassed in motor-homes or commercial trucks in France, and the warning put out by the Foreign Office for travellers to be aware of this danger, this College remains of the view that this is a myth. It is the view of the College that it would not be possible to render someone unconscious by blowing ether, chloroform or any of the currently used volatile anaesthetic agents, through the window of a motor-home without their knowledge, even if they were sleeping at the time. Ether is an extremely pungent agent and a relatively weak anaesthetic by modern standards and has a very irritant affect on the air passages, causing coughing and sometimes vomiting. It takes some time to reach unconsciousness, even if given by direct application to the face on a cloth, and the concentration needed by some sort of spray administered directly into a room would be enormous. The smell hangs around for days and would be obvious to anyone the next day. Even the more powerful modern volatile agents would need to be delivered in tankerloads of carrier gas by a large compressor. Potential agents, such as the one used by the Russians in the Moscow siege are few in number and difficult to obtain. Moreover, these drugs would be too expensive for the average thief to use. The other important point to remember is that general anaesthetics are potentially very dangerous, which is why they are only administered in the UK by doctors who have undergone many years of postgraduate training in the subject and who remain with the unconscious patient throughout the anaesthetic. Unsupervised patients are likely to die from obstruction of the airway by their tongues falling back. In the Moscow seige approximately 20% of the people died, many probably from airway obstruction directly related to the agent used. If there was a totally safe, odourless, potent, cheap anaesthetic agent available to thieves for this purpose it is likely the medical profession would know about it and be investigating its use in anaesthetic practice.

ADDITION: The portable gas alarms are not intended for narcotic gases, but should warn the user of toxic fumes endangering your air passages (caused by combustion like a fire with burning plastic e.g. hydrogen cyanide, hydrogen chloride/fluoride), choking gases (carbon dioxide, carbon monoxide) and explosive mixtures (Butane, propane).