Why does the alarm on my 2011 Ford Fiesta keep going off?

I just bought a used 2011 Ford Fiesta. I m used to regular keys and keyfobs for the locks, but this has keyless entry/ignition.

I just got this car home and locked it before going into my house, and 3 times now I ve heard the alarm go off, and when I go out to see what s going on the lights are still flashing and the alarm is getting quieter (if not totally silent) (and the lights are still flashing).

I ve been hitting the unlock/lock buttons on my keyfob to make it stop but I still don t know why the alarms are going off in the first place.

Read more: Why does the alarm on my 2011 Ford Fiesta keep going off?