Skylink WT-433W Wireless Door & Window Burglar Alarm Alert Security Sensor | Affordable, Easy to Install DIY Accessory for SC Series Systems NO MONTHLY FEES and easy DIY (Do It Yourself) installation MONITORS DOORS AND WINDOWS with opened or closed signal WIRELESS - BATTERY POWERED with low battery indication: be informed when the sensor`s battery is low before it stops sending signals COMPATIBILE with SC-10W, SC-100W, SC-1000W systems. LIFETIME SUPPORT - Toll free 1-800-304-1187, support@skylinkhome.com