Aico EI146 Optical Mains Smoke Detector 240v. Best deal at only £18.50. Alkaline Battery Backup; Interlinkable with other Aico EI range smoke and heat detectors; More responsive to slow smouldering fires; Separate mains and warning LEDs; Time and money saving Easi-Fit design; Alkaline battery supplied already connected; 5 year guarantee.