Mine does that. Know idea why.
Sometimes, to lock it, I hit the button while
walking away,.. I won't hear it chirp. Of course
I then hit the button again,.. Nothin. no chirp.
Hit the button a THIRD time and there it goes!
The alarm goes off! But, what is happening I think,..
Is that each of the 2 prior times that I hit the button,
the alarm is really being set. (Because, I can look into
the truck & see the alarm-light on the dash blinking).
The third hit of the button sets it off. So, sometimes it
chirps while setting the thing. Sometimes it doesn't.
But, it's always setting it reguardless.