The Ei151 is a mains powered smoke alarm with a lithium back-up battery. As the Ei151 is now discontinued, Ei Electronics (also known as Aico) have developed the Ei3016 optical smoke alarm as the most suitable replacement because it can interlink with any Ei150 series alarms remaining in your system. The rectangular base and connector of the Ei151 is no longer supported and will need to be replaced by an electrician to use your existing wiring. This replacement alarm will be supplied with a masking plate to negate the need for painting and an easichange tool. The Ei3016 features new optical sensor technology that is less prone to false alarms than the ionisation technology of the Ei151, making it suitable for use in a wider range of locations. Bedrooms, hallways, landings and living areas, plus rooms adjacent to kitchens (but not within kitchens) are all perfect locations for the Ei3016. A rechargeable lithium back-up battery will ensure you remain undisturbed by low battery warnings for up to 10 years.