Vaping around smoke detectors can cause some confusion - can e-cigarettes really set off the fire alarms? Technically, yes they can. There’s many different ways that you can set off a smoke detector – we've all probably heard of people setting smoke detectors off with dust, not just smoke.

So how come water vapour is setting off smoke alarms?

The answer is not so complicated, but requires a basic understanding of all the different types of smoke & fire detectors. Most commonly used smoke detectors in homes and restaurants use an optical photoelectric type sensor that is set off when smoke obstructs the air in front of it. This means you can throw water or any fine type sand or dirt into the vent and it will also set it off. These are the cheaper type smoke detectors you can purchase at any hardware store for example. Therefore, if a thick cloud of vapour is blown into the detector, it can be enough to obstruct the optical mechanism and set it off, without any actual presence of smoke. What's also worth mentioning, it's the heat smoke alarms, which are usually used in kitchens. However, they are triggered by heat and not smoke so are unlikely to detect vapour from electronic cigarettes.  

Another similar type of technology is  the air ionization detection system that is triggered when smoke enters and changes the ions present in the air surrounding the detector. This system is also very popular and has a similar function and response time time to an optical detector. However, things get a bit more complex when we look at all the other types of alarms, such as CO2 carbon monoxide detection. These types of systems will measure how much CO2 emission is present in the surrounding air, but are not typically used to alarm of fires due to the slow response time.  

Out of all types of alarm listed above, it is the optical alarm which is most likely to be triggered from e cigarette vapour. That said however, ionisation alarms are also known to have been set off by vapour produced from the electronic cigarettes e liquid.

The vapour from ecigs does set off smoke detectors, but only when exhaling or blowing the vapor towards the smoke detector at close proximity. It’s not much different than smoking a cigarette in that regard. Vapour is less likely to set off a smoke alarm though, because unlike smoke, vapour disperses quickly – so don’t worry too much about it.