ADT is the largest professionally monitored home security company in the U.S., serving approximately 6.1 million residential and small business customers. ADT installs sensors, cameras, and smart home devices in homes and small businesses, then provides 24/7 monitoring from its network of monitoring centers — when an alarm triggers, ADT contacts first responders and the customer. The vast majority of revenue is recurring monthly fees for monitoring and related services, with annualized recurring monthly revenue of ~$4.3B representing roughly 85% of total revenue. Most new customers subscribe to ADT's proprietary ADT+ platform, which layers smart home automation — remote access, live video, smart locks, and thermostats — onto the core security system. ADT reaches customers through direct sales (phone, door-to-door, e-commerce), a network of ~140 authorized dealers, and bulk purchases of existing monitored accounts. The core economics involve meaningful upfront installation costs that ADT recoups over roughly two years, after which the recurring fee generates durable returns over a typically long customer relationship. Key profitability drivers are attrition rate, new subscriber additions, average monthly revenue per subscriber, and subscriber acquisition cost efficiency. ADT is expanding into DIY self-install security under the "ADT Blue" brand, small business, and aging-in-place health monitoring. In February 2026, ADT acquired Origin AI for $170M, adding Wi-Fi-based ambient sensing technology to detect human activity without cameras, which ADT plans to integrate into ADT+ for commercial launch in 2027.