Makes no sense.
Why on earth did the mother keep leaving her phone in the car? Absolutely retarded.
In an earlier scene the husband calls and says he's been calling for awhile with no answer and she says sorry that she kept her phone in the car.
Then when the noises start she goes to the house phone but it isn't working so she runs out to the car looking for her cellphone.
Why did she put the cellphone back in the car? Who the fvck does that? Stupid movie for making characters do unrealistic things.