Skylink AA-433W Wireless Back-Up/ Secondary Security Burglar Alarm Accessory for SC Series  & AAA+ Systems. NO MONTHLY FEES and easy DIY (Do It Yourself) installation LOUD 110 DECIBEL SIREN . Activated by keychain transmitter 4B-433W or Skylink Control Panel SC-001, AM-100 or ML-100 FOR INDOOR operations only. Operating range up to 100 feet in an open area EXPANDABLE to trigger this back-up siren when 1 of 15 different paired sensors is activated. LIFETIME SUPPORT - Toll free 1-800-304-1187, support@skylinkhome.com