The Strangers

James (Scott Speedman) and his girlfriend Kristen (Liv Tyler) arrive at James' childhood summer home, tired and irritable after a long evening at a friend's wedding reception. It is revealed that while they were there, James proposed to Kristen and she refused, claiming she is not ready for marriage yet. James calls his friend Mike to come pick him up in the morning.
Shortly after 4 a.m., there is a knock at the door, surprising to them both since the house is so remote and far from any civilisation for miles. They open the door and a young blonde woman, whose face is obscured by low lighting, is standing on the porch asking for Tamara. When told that she is at the wrong house, she asks if they're sure, then leaves with the casual caveat that she will "see them later".
Due to the tension between him and Kristen, James leaves to go for a drive and to buy cigarettes. While alone in the house, Kristen hears another knock at the door; she refuses to open it after realising that it is the same woman from earlier, who has returned to ask for Tamara again. She leaves. Kristen then starts hearing strange noises around the outside of the house and her cell phone goes missing. She calls James using the house phone but the line goes dead. The smoke alarm goes off and Kristen disarms it as there is another loud bang on the front door. She goes to the kitchen and grabs a large knife. When she returns, the smoke alarm cover has been placed on one of the chairs, so Kristen knows somebody has been inside. When she hears a noise from the back yard, she goes to the back door and opens the curtains to find a man wearing a sack mask staring back at her. Panicked, she hides in the bedroom until James returns.
When James arrives back, she explains what has happened and he goes to investigate. He finds his car ransacked and the blonde woman, now wearing a doll mask, watching him from afar in the street. His phone has had its battery stolen and he realizes the house has been breached. The couple attempt to leave in James's car but a third stranger wearing a pin-up girl's mask drives a pick-up truck into the back of them, totaling it and forcing them to flee. Back in the house, Kristen and James find a shotgun and they wait for one of the intruders to come into view.
At the same time, Mike arrives to pick James up and realises something is wrong after seeing the smashed car. He goes inside and James, mistaking him for one of the intruders, shoots him dead. A devastated James then remembers an old radio transmitter in the backyard shed. He leaves the house and encounters the blonde woman. When James tries to shoot her, the masked man intervenes and knocks out James. Kristen hears the shot and runs to the shed. She finds the radio and tries to contact someone for help. Before she can, Dollface appears and smashes the radio. Kristen rushes back to the house, where she is confronted by the blonde woman, who is now armed with a knife. The masked man then arrives with the captured James and the gun, who incapacitates Kristen. Both James and Kristen are now unconscious.
When James and Kristen wake up, they are tied to chairs in the living room with the masked strangers standing before them. Kristen asks them why they are doing this and the blonde woman replies "because you were home". The strangers then unmask themselves to the couple (not to the audience) and begin stabbing Kristen and James before leaving in the pick-up truck. As they drive away, they drive past the two young boys from the opening, who are distributing religious tracts. Dollface gets out of the truck to ask for a tract. The boy asks her if she's a sinner and she replies, "sometimes". When she returns to the car, the Pin-Up Girl tells her "It will be easier next time."
The two young boys come to the house, finding the destroyed car in the yard and the front door open. They enter the house and discover the bodies of Kristen and James. Kristen, who is still alive, wakes up and screams.

Question: What happened to James's phone?
Answer: Battery stolen