Part B of the building regulations, which came into effect on 1 June 1992, sets out the requirements in relation to fire safety in the design and construction of new buildings and the extension of, or material alteration to, existing buildings. Houses built and-or extended in accordance with the 1991 edition of Technical Guidance Document B – which provides guidance on how to comply with the regulations – should be fitted with battery operated smoke alarms. Battery operated smoke alarms are cheap to buy – less than £10 – and easy to install. However, householders often forget to check that the batteries are operating. For example, only three-fifths of householders in the survey referred to by the Deputy had checked their smoke alarms within the past 12 months. Once the batteries run out, the smoke alarms become inoperative. For this reason, I published a revised and upgraded Technical Guidance Document B (Fire Safety) in December 1997, which recommends that houses built and-or extended on or after 1 July 1998 should be fitted with mains operated smoke alarms, rather than battery operated alarms.