About US


Guardian Security Training provides New York State approved security guard training courses for Long Island and NYC. GST is the only training facility on Long Island to offer not only security guard courses, but private investigator development, HR218, conceal carry courses, and active shooter response seminars and drills.


Our mission is simple: To provide high quality education to build up qualified candidates, resulting in quality protectors for our community.


Matthew D. Seifer

Licensed Private Investigator, DCJS Certified Instructor, Expert Criminal Defense Investigator, NYS Registered Armed Guard, US Army Veteran

Matthew D. Seifer is the co-founder of Guardian Security Training and Radius Investigations. Seifer has been a self-employed business owner throughout the last 26 years. His entrepreneurship includes over a decade as a private investigator and qualifying officer of a private investigations firm, and operating a security guard agency for over 15 years.

Through his relationships with businesses and government personnel, reputation for professionalism and integrity, and continuous tenacity, Mr. Seifer has grown his work from a self-employed private investigator, to a full private investigation agency, and formed security and public safety training facility.

His extensive investigative skills, as well as his decades of first-hand experience in armed private security and overseeing teams of operatives, has shaped him into a valuable wealth of knowledge in the subject matters of private investigations and conducting oneself as a security guard.


Our quality professional instructors come from a range of backgrounds: Private Investigations, Law Enforcement, Federal Agents, and Military.

Marc Martinez

Marc Martinez

Co-Founder, Licensed Private Investigator, NYS Registered Armed Security Guard, Expert Criminal Defense Investigator

Marc Martinez is a licensed private investigator with over a decade of investigative experience. Through his close connections with security agencies throughout New York, Mr. Martinez ensures that all security guards that are employed by these companies have properly trained security professionals.

Marc D. Martinez is the owner of Marc David Investigations. He began his career over 27 years ago, investigating city corruption, fraud related offenses, government waste, and large scale bribery. He operated as an undercover and surveillance investigator, where he learned his craft conducting various types of investigations. Later, Mr. Martinez went on to be a loss prevention manager and security threat assessment professional.

From 2005 to 2008 Mr. Martinez was the manager of a mid-size Investigations firm, Guardian Safety Associates, where he oversaw all day-to-day operations and managed the company’s major contracts and investigative staff.

Martinez was introduced to executive protection and personal security, where he gained extensive experience providing security consulting, security threat assessments, and personal protection services. Mr. Martinez has conducted numerous executive protection details and private security functions that have included working alongside federal agents and NYPD protecting politicians, dignitaries, public figures, high profile celebrities, government establishments, industry and in the private sector.

Currently, Mr. Martinez is a criminal defense investigator for defense attorneys in the Nassau County area as well as an expert investigator for Nassau County defender plan, 18-b Investigations.  

Since 2012, Mr. Martinez has had a professional and personal relationship with who he believes is an outstanding investigator, Matthew Seifer of Radius Investigations. Martinez has gained and benefited by the relationship with Mr. Seifer, and subsequently joined forces with Seifer in 2018 to establish Guardian Security Training,  to offer the public and ex-Law Enforcement years of expertise in the security field.

Dwight Hovington

Dwight Hovington

DCJS Certified General Topics Security Guard Instructor, Licensed Private Investigator, Crisis Prevention Intervention, Active Shooter Training

Dwight Hovington is a retired and highly decorated New York City Police Detective Investigator. He was responsible for investigating complex cases of organized crime which resulted in the arrests and prosecution of individuals charged with federal, state, and local crimes.

Mr. Hovington received his specialized training from the NYPD and the United States Secret Service in Dignitary Protection and fraud investigations. Through his robust background, he has extensive years of experience in civil, matrimonial, insurance, and corporate investigations. His previous experience also includes having the responsibility for the protection of numerous dignitaries and celebrities abroad. As a licensed private investigator, Hovington specializes in surveillance, background and due diligence investigations, infidelity cases, executive protection, and threat assessments.

Hovington’s expertise covers the general topics in the security guard training curriculum, as well as the introduction to private investigations course.

Don Lettieri

Don Lettieri

NYS DCJS Certified General Topics and Armed Security Guard Instructor, Utah Conceal Carry Instructor, NRA Firearms Instructor & Training Counselor, NYS Registered Armed Guard, USAF Veteran, Retired Federal Officer

Don Lettieri is a US Veteran and retired Federal Officer from the US Department of Justice and the Federal Bureau of Prisons. In his 23 years of service, Lettieri provided firearms and less than lethal munitions training for the Justice Department. With Mr. Lettieri’s decades of experience in firearms instruction, he has received his professional instructor certifications from agencies including the NRA, NYS Division of Criminal Justice Services, and Utah Department of Public Safety.

Mr. Lettieri instructional methodology is to always provide instruction that follows the student’s pace. He has trained those from the most novice to seasoned officers in the safe and proper handling of firearms.

Lettieri is the top professional in providing instruction for general security guard topics, armed security guard courses, firearms training, and Utah conceal carry weapons courses.

Jason Green

Jason Green

NYS DCJS Certified General Topics and Armed Security Guard Instructor, LEOSA HR218 Instructor, Instructor in Defensive Tactics, ASP Tactical Weapons, Handcuffing Aerosol Subject Restraint, Texas A&M CRASE, Glock Advanced Armorer

Jason Green has an exhaustive list of experience and accolades too long to list in a quick biography: A summary of his work includes over 2 decades of Firefighting and Emergency Medical Technician experience. Mr. Green has several instructor certifications, including fire service, NYS DCJS Instructor certifications in general topics as well as law enforcement training, and active shooter response. 

As a member of the Law Enforcement Trainers and Educators Association, Mr. Green  emphasizes quality education for those who serve in law enforcement, as well as the general public in matters of proper safety and security procedures.

Green’s specializes in providing instruction for armed security training, LEOSA HR218, Handcuffing and Aerosol Restraint training, and unarmed security guard courses. 

Certified by
New York State

We are fully certified by the New York State Division of Criminal Justice Services as an Approved Security Guard Training School


150 Motor Parkway, Suite LL20
Hauppauge, NY 11788


83-20 Queens Blvd,
Elmhurst, NY 11373

With several locations to choose from on Long Island and NYC!