Panic Room - What Did I Miss ????

[Gizmonster]

Just watched Panic Room on Film4 (seen it before but it was aaaaages ago, so I thought I'd watch it again), but something's bugging me:

How come the police turned up at the end ??

When the police turned up to the house the first time and the officer said something along the lines of, "you can give me a sign like blink your eyes if you can't say anything and there's something wrong". Well, Jody Foster just stared at the officer without blinking or giving him any sign; so how come the police turned up when they did ??

[ChillDoubt]

Last paragraph:

http://en.wikipedia.org/wiki/Panic_Room#Plot

[Gizmonster]

Thanks for the link, but I'm not convinced to be honest.
I know that the police got a phone call, which alerted them in the first place, but I'm not convinced by the explanation:
"The police, alerted by Meg's suspicious behavior earlier, arrive in force and capture Burnham ........ "