STARPOINT Extra Add-On Window/Door Sensor for the STARPOINT Expandable Wireless Multi-Unit Long Range Doorbell Chime Alert System, Model LD, White AS SEEN ON BUSINESS INSIDER, FOX, ABC, NBC & CBS News - "It's built well, and it has a nice minimalist style" - Business Insider, 08/21/15. Our doorbells are great looking, loud, and reliable. The STARPOINT L Series is a CONFIGURABLE and EXPANDABLE doorbell system that can EASILY ADD on 20+ more extra receivers, transmitter buttons, motion sensors and door sensors. Custom build your own system that fits for your needs. Easy to use pair-able random generated frequency code technology allows you to mix and match L Series components easily with one or multiple receivers. Multiple receivers can be configured to RING WITH DIFFERENT chimes/ringtones to let you know which transmitter was triggered _- a very convenient feature for multiple doorway entries. Built in receiver MEMORY feature RETAINS doorbell chime/ringtone selection even when receiver is unplugged or powered off. Long range operation with the receiver at over 500 feet Includes 1 extra remote window/door sensor, double sided sticker, AA battery is included. DOWNLOAD OUR "10 MORE WAYS TO USE SADOTECH DOORBELLS GUIDE - Did you know that our customers use SadoTech doorbells to train dogs, teachers love using it to quiet down classrooms, seniors and disabled use SadoTech doorbells as assisted living call pagers, and more! SCROLL DOWN on this page to the Technical Specs section below and click the Application Guide link to DOWNLOAD the PDF file. Open it with Adobe Acrobat Reader. WANT TO LISTEN TO OUR CHIMES/RINGTONES BEFORE YOU BUY? GO AHEAD - Just SCROLL DOWN to the Technical Specs section below and click on the Specification Guide link to DOWNLOAD the PDF file. Open it with Adobe Acrobat Reader to play all 52 ringtones. We are proud to announce we developed a custom music chip in our doorbells that includes carefully selected. Over 50+ different ringtones. Operating range of over 500 ft (1000 ft in open area). 4 levels of adjustable volume from 25db - 110db.