Brosnan Security provides security services and guards in Chicago, IL. Brosnan is full-service investigative, protective and intelligence firm to a global network of clients. Headquartered in New York, with branch locations in multiple states, Brosnan is one of the largest privately held providers of technology-driven security services. With more than 500 years of law enforcement experience, Brosnan understands the law, and more importantly, law breakers. We protect your people, property and assets for aggressive risk mitigation strategies and technologies. Brosnan is a technology-driven best-in-class security provider.