AAA batteries were originally developed in 1954 for the purpose of reducing the size of cameras. Over time, the size became one of the most popular types of batteries available. The American National Standards Institute (ANSI) formally recognized the AAA size of batteries in 1959. This for all intents and purposes permanently established the AAA as what we know and commonly recognize today.
Needless to say, AAA batteries are extremely common. They are used in all sorts of portable and handheld electronic devices, and they are loved for their small size and overall ease of use. Everything from TV controllers, handheld gaming consoles, calculators and electronic razors and toothbrushes uses AAA batteries. And with this immense popularity, AAA batteries are very easy to obtain, and they can be found in almost any store.
As for the security industry, AAA batteries definitely fulfill a niche. They are often used in the thin "slimline" door and window contacts, when other cylindrical batteries like the CR123A and AA batteries are too wide. Since security sensors don't usually require large amounts of power, AAA batteries serve a role when a coin battery like a CR2032 or CR2025 just isn't enough.
It's not too hard to find examples of security sensors that use AAA batteries. Some examples include the Honeywell 58020L and the Honeywell 5818MNL. The lifespan for AAA batteries greatly depends on the type of device that is being powered. We advise users to use lithium AAA batteries over alkaline batteries, since they will provide a longer product life. Users should also be aware that some devices may require multiple AAA batteries.