In protecting executives and their families at home, prime consideration is given to the protection of life and the prevention of injury rather than the protection of property. Because executives and their families often underestimate the terrorist threat and regard security precautions as a nuisance, the security engineer must assess the family's routines and work to increase the security awareness of family members. Major elements of a residential security system should include perimeter barriers such as walls or fences; hardening of the outer shell to increase escape time, including sensors and annunciators and replacement of doors and windows with materials that will minimize delay during escape, and intermediate interior barriers such as steel doors with deadbolt locks. In addition, interior safe havens (windowless rooms with steel-lined walls, communication equipment, and breathing apparatus) should be provided. Finally, the security engineer must ensure that the family understands the system, is willing to become a part of it, and has a positive overall reaction to it.