A few weeks ago I was cat sitting for a long time client with a house alarm. I went in that morning and it was super hot in the house, so I tried to open the back window. Either I was too hot or it was too heavy, but I gave up and just closed it. I did my rounds (meds, food, litter, love) and set the alarm and left. This was about 8am. My next two stops were on the street behind him. I finished those up (both have alarms as well) and continued on with my day.
I received a phone call from the owner of the first house around 11am stating that the contractor next door told him that the alarm was gong off and the police came! He asked if I could go back over and take a look to make sure the alarm was set properly and that the house was intact. I headed straight there from the dog that I was with. I went in, shut the alarm off, looked around for broken windows, etc. - and saw nothing out of the ordinary. I called him to let him know and as I am on the phone with him, I hear a knock at the door. While on the phone with him, the police came back! They were in plain clothes and they flipped their badges at me. They said, "You know the alarm was going off..." I explained that I am the pet sitter, on the phone with the owner of the house if they wanted to talk to him (they didn't), and that everything was fine. They took my ID to run it as proof that I was there and explained that they were in plain clothes in a pickup truck because they were actually trying to catch a real burglar in the neighborhood! Awesome. Because then I had to leave and NOT set the alarm due to all of the mishaps of the morning.
All in all - it was damn awkward and I felt like a criminal for doing my job. The moral of the story is that I loathe alarm systems. They are a necessary evil, I get that - but I fear them for this very reason.