Timecrimes

In the Spanish countryside, a middle-aged man named HÃ©ctor (Karra Elejalde) and his wife (Candela FernÃ¡ndez) live in a home that they are renovating. HÃ©ctor scans the forest behind their house with binoculars and sees a young woman take off her t-shirt, exposing her breasts. When his wife goes shopping, he investigates and finds the woman on the ground, naked and unconscious. He is then stabbed in the arm by a mysterious man with pink bandages on his face. Fleeing and breaking into a mysterious nearby building, HÃ©ctor contacts a scientist (Nacho Vigalondo) by walkie-talkie, who warns him of the bandaged man and guides him to his location, promising safety. The scientist convinces HÃ©ctor to hide from the bandaged man, who is just outside, in a large mechanical device. However, when he leaves the machine, HÃ©ctor discovers that he has traveled approximately an hour back in time.
The scientist explains that the machine is an experimental time travel device, and refers to HÃ©ctor as "HÃ©ctor 2". The scientist tells him that they need to stay where they are and let events unfold. Despite the scientist's warning, HÃ©ctor 2 drives off in a car, passing a cyclist, only to be run off the road by a van, cutting his head, which he wraps using the bandage from his arm wound. The bandage turns pink from absorbing the blood. The cyclist approaches to see if he is all right - it is the woman he earlier saw in the forest. He proceeds to replicate events by making her undress in view of HÃ©ctor 1. When she runs away, he catches her, inadvertently knocking her out. He lays her out naked on the ground and then stabs Hector 1 in the arm when he arrives. The woman escapes. HÃ©ctor 2 returns to his home, where he hears a scream and chases a woman through his house and onto the roof. When he attempts to grab her, she slips and falls to her death. Seeing the body from the roof, HÃ©ctor 2 is horrified, believing he has killed his own wife.
HÃ©ctor then contacts the scientist over a walkie-talkie and convinces him to lure HÃ©ctor's past self to the lab with warnings that he is being pursued. Driving to the lab, HÃ©ctor 2 insists that he must travel back one more time, despite the scientist revealing that there is a HÃ©ctor 3, who told him he must stop HÃ©ctor 2 from doing just that.
After removing his bandages, Hector 3 convinces the scientist to send him back several seconds before HÃ©ctor 2 appears. He finds a van and runs HÃ©ctor 2 off the road, but crashes as well, knocking himself out. Upon waking, he informs the scientist he has failed and to stop HÃ©ctor 2 by any means. He encounters the woman again, startling her into screaming, though she does not recognize him as her assailant. Since HÃ©ctor 2 has heard her scream, HÃ©ctor 3 and the woman flee to HÃ©ctor's house. They become separated. HÃ©ctor 3 finds and hides his wife, then realizes what has to happen / will happen / has already happened. He finds the woman, cuts her ponytail off, gives her his wife's coat, and tells her to hide upstairs. HÃ©ctor 2 chases her onto the roof. HÃ©ctor 3 sits on his lawn with his wife, as HÃ©ctor 2 accidentally kills the woman, then drives off. Emergency vehicles are heard approaching in the distance.

Question: How does Hector contact the scientist?
Answer: walkie-talkie