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Guardian Security Services

(631) 351-6473
Guardian Security Services


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Founded in 2007 by Matthew D. Seifer, Guardian Security Services has established itself as a trusted name in the field of private investigations and security. With nearly three decades of experience and a reputation for professionalism and integrity, Matt brings a unique blend of expertise to his work. As a U.S. Army veteran with more than 26 years in the private sector, he goes beyond the role of a typical private investigator. Matt has evolved into an instructor and mentor, dedicated to providing safety and security to the public. His contributions have been recognized by local and national media platforms, including Inside Edition, which featured him for his active shooter response training and drills for schools and workplaces.

Matt's extensive skill set encompasses a wide range of sensitive and complex investigations. From covert surveillance to locating missing persons and securing crucial evidence for trial preparation, he has proven himself as an expert criminal defense investigator for the Nassau and Suffolk County Criminal Courts. In addition, Matt excels as an investigative case manager, adept at assembling and leading teams of specialized investigators to achieve clients' objectives efficiently. These teams consist of retired law enforcement, military personnel, computer forensics experts, and counter-surveillance specialists.

To ensure comprehensive coverage across the United States, Matthew has built a network of specialized investigators in all 50 states, allowing Guardian Investigations to promptly respond to clients' needs nationwide. Within the agency, Matt assumes the role of counter-surveillance and technical surveillance counter-measures (TSCM) expert. Leading the firm's operations in detecting and neutralizing covert surveillance, he diligently protects clients' privacy by locating and eliminating threats such as GPS trackers, hidden cameras, and hidden recording devices.

Described as a strong and natural born leader, Matt is also known for his compassion, dedication, and trustworthiness in all his interactions with clients, students, and the community. He personally oversees every case, ensuring that clients receive the answers they need to make informed decisions. Since its establishment, Guardian Investigations has expanded beyond its Long Island headquarters to New York City and has developed a global network of private investigators. Under Matthew's professional expertise, the agency has evolved into an exceptional PI agency, offering a broad spectrum of services ranging from background investigations to TSCM bug sweeps and insurance investigations. Additionally, they have launched Guardian Security Training, a training division dedicated to providing unique educational programs on security, safety, and private investigations.


  • Accident / Reconstruction
  • Arson / Fire
  • Asset Search
  • Background Checks
  • Bug Sweep / TSCM
  • Child Support / Custody
  • Civil
  • Computer Forensics / Crime
  • Crime Scene
  • Criminal
  • Domestic
  • Due Diligence
  • Electronic Data Discovery
  • Executive Protection
  • Forensic
  • Fraud
  • Infidelity / Cheating Spouse
  • Insurance
  • Judgment Recovery
  • Missing Persons
  • Process Service
  • Public Records
  • People Locate / Skip Trace
  • Social Media
  • Surveillance
  • Workers Compensation
  • Wrongful Death

Service Guarantee

All investigations performed with discretion.

We are available 24 hours a day!

Areas of Coverage

  • New York City, NY
  • Bronx, NY
  • Brooklyn, NY
  • Manhattan, NY
  • Queens, NY
  • Staten Island, NY
  • Nassau County, NY
  • Hempstead, NY
  • Mineola, NY
  • Uniondale, NY
  • Levittown, NY
  • Bellmore, NY
  • Plainview, NY
  • Garden City, NY
  • East Meadow, NY
  • Freeport, NY
  • New Hyde Park, NY
  • Wantagh, NY
  • Manhasset, NY
  • Westbury, NY
  • Farmingdale, NY
  • Great Neck, NY
  • Long Beach, NY
  • Oceanside, NY
  • Glen Cove, NY
  • Massapequa, NY
  • Valley Stream, NY
  • Rockville Centre, NY
  • Marrick, NY
  • Syosset, NY
  • Lynbrook, NY
  • Suffolk County, NY
  • Babylon, NY
  • Brookhaven, NY
  • East Hampton, NY
  • Huntington, NY
  • Islip, NY
  • Riverhead, NY
  • Shelter Island, NY
  • Smithtown, NY
  • Southampton, NY
  • Southold, NY
  • Connecticut, NY
  • New Jersey
  • Nationwide
  • International


  • PInow
  • Association of Certified Fraud Examiners
  • Nassau County Bar Association
  • Better Business Bureau
  • Veteran Owned Business

Contact Info

(631) 351-6473
940 Grand Blvd
Deer Park, NY 11729

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Office Location

940 Grand Blvd
Deer Park, NY
(631) 351-6473

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