You need the Home Base, either one but now get home base 3 as home base 2 will soon be not for sale anymore and all equipment will be transferrable to home base 3.
This sensor can be put on any door or window simply with the included double stick tape. Works on gates, doors, sliding doors, any window, hatch, etc. Integrates with my Google Home app and Eufy app. Can make it beep when opened/closed and trigger an alarm via home base that's approximately 100db loud when alarm is armed. Only downside is the alarm goes off if sensor tripped is closed. Disabling the alarm tone. Wish it stayed going until manually silenced in app by user. Eufy really should update via firmware this glitch. Otherwise, works great, easy to install and sync to home base and Google . Takes 1 AA battery which lasts 2 years they say. Better than recharging every month.