So what's the difference between a fog and smoke machine? Well, a smoke machine is generally what you'd see on a night out in a club, or at your uncles Halloween party - the smoke machine works by passing a liquid (typically water and glycerin or propylene glycol) through a heat exchanger - this is then fed out of a nozzle! Voila - you now can't see your feet in the nightclub and you have an eery 'low hang' smoke cemetery vibe to your house. But wait, all my valuables are up on shelves - I'm not bothered about securing my shoes!
This is where fog machines are different, artificial fog is actually exactly the same as naturally occurring fog (just denser if you are using a Fog Off system). The 'fog liquid' is the same as the smoke liquid with a small difference in water content - the difference is in the way the system heats it. The liquid is passed through a super heated chamber at a high pressure and temperature and shot out through the nozzle into the air - this creates a lighter partical weight than the heavy smoke partical, meaning you get a thick long-hanging fog that doesn't settle on the ground like smoke does. This protects not only your shoes; but everything from your floor to your ceiling making it perfect for securing your belongings and assets.
A small side note that although a fog machine may set off a smoke alarm, this is only due to the way smoke alarms detect chemical changes or optical changes - there's a 50/50 chance with a chemical sensor depending on how much fog is concentrated near it. Optical sensors will absolutely be set off purely due to the nature of the system.