I decide to implement access log. Now, when someone enable or disable the alarm, the arduino calls a script on a remote web server (the same I use to send mail, I changed it adding some parameters) and record time and action in a txt file.

An example of the record is:

2014-8-20 19:53:3 - XXX enabled the alarm
2014-8-20 19:53:10 - XXX disabled the alarm