This listing is for one:

Brand New In Box, Genuine, Authentic

SimpliSafe (MS1000) Original Generation Motion Detector Sensor

Battery Included with Intact Battery Pull Tab

Mounting Screws Included

Please Note: Compatible With Original Generation Simplisafe System

WILL NOT WORK WITH 3RD GENERATION SYSTEM

Feel free to contact me with any questions, including compatibility concerns

Thank you for checking out my listing!