Hydrofarm Analog CO2 Controller with Remote Probe - Autopilot APCECO Offers indoor gardeners an economical and simple method of monitoring and controlling CO2 within the grow area Utilizes a highly visible and intuitive LED indicator display LED indicator will blink to show the PPM level in increments of 100 15' remote sensor allows versatile placement within the grow area Built-in photocell automatically deactivates at nighttime