Because me and my girlfriend are lazy we have a cleaner who comes every two weeks. We pay for 2.5h but sometimes things were still spotty so we were wondering if they're actually here all that time. After "can't your just build something to figure that out" + a couple hours i had a proof of concept that sent me SMS messages every time the cleaner was there and left. My 15min algorithm for tracking presence wasn't exactly perfect and i ended up getting hundreds of "THE MAYANS ARE COMING!!" SMS messages. I ended up paying for all of these but found out the cleaner was there 2:27 (her name is Maya).

Having worked previously on a project requiring cellular connectivity i used the SM5100B. The datasheet is notoriously incomplete/wrong here so i had fought through a lot of issues to get things running. Because of this i already had the basic building blocks for connectivity and it was trivial to just add a PIR sensor. 

For Captain Pugsley i wanted to improve on a couple things:

1) Wifi instead of cellular (free)

2) Nicer form factor (no Arduino wire mess)

3) More reliable & accurate

4) Option for remote control

5) Keep the attitude!

For motion tracking PIR was a fairly obvious choice. They're cheap, reliable and easy to use. The PIR requires a lens though which would have to be visible. I took this as a design opportunity and started thinking of options that include a dome. A UFO came up fairly quick. Inside this small UFO is Captain Pugsley who's sole mission is to monitor your house. Perfect!