matthew seifer radius investigations private investigator long island

Matthew Seifer

Licensed Private Investigator

Registered Armed Guard

Technical Surveillance Countermeasure (TSCM) Specialist

Expert Criminal Defense Investigator

NYS DCJS Certified Instructor

Matthew Seifer founded Radius Investigations in 2007. Seifer has an extensive background in private investigations and security, with over a decade of experience in these industries, earning him a reputation for professionalism and integrity. Seifer is a U.S. Army veteran, with over 26 years in the private sector. He is not your typical PI: his work in security and education has made him evolve into not just a private investigator, but an instructor and mentor to help provide safety and security to the public. Matthew Seifer has been featured on local and national media platforms, including Inside Edition, for his work in providing active shooter response training and drills for schools and the workplace.

Matthew has been responsible for handling a wide variety of sensitive and complex investigations, including covert surveillance, undercover investigations, locating missing persons (including witnesses and adversaries for service of process), and securing key evidence for trial preparation. As an Expert Criminal Defense Investigator for the Nassau County Criminal Courts, he is key in assisting clients during litigation cases. Matthew is also an accomplished investigative case manager and leader for teams of expert investigators. He has a great deal of expertise in assembling and managing teams of specialists representing a wide array of investigative skill sets in order to pursue the clients’ objectives in the most efficient and effective manner possible. Matthew’s investigative support teams include retired law enforcement, military personnel, computer forensics experts, and counter-surveillance specialists. Matthew has developed a network of specialized investigators in all 50 states in order to ensure that Radius Investigations can respond to our clients’ needs anywhere in the country.

Seifer is Radius Investigations’ counter-surveillance and technical surveillance counter-measures (TSCM) or “bug sweeping” expert. He leads the firm’s operations in searching for, identifying, and neutralizing all forms of covert surveillance which may intrude on our clients’ privacy, including GPS trackers, hidden cameras, and “bugs” or hidden recording devices.

Mr. Seifer is described as strong and a born leader, as well as compassionate, dedicated, trustworthy, and diligent with his clients, students, and community. He oversees every case and will follow through until the client has the answers they need to make an educated and informed decision.

Since the inception of Radius Investigations, Seifer has expanded the agency from his Long Island, New York headquarters to New York City and has developed a world-wide network of private investigators. Seifer’s professional expertise has made Radius Investigations not your typical PI agency: Providing a broad spectrum of services including background investigations, TSCM bug sweeps, insurance investigations, as well as unique educational programs on security, safety, and private investigations through their new training division, Guardian Security Training.

About Radius Investigations

“Not Your Typical Private Investigation Firm”

Radius Investigations, centrally located on Long Island in Hauppauge, NY, was formed in 2007 by Matthew Seifer, a Licensed Private Investigator, Registered Armed Guard, and Division of Criminal Justice Services (DCJS) Certified Instructor.

We have established ourselves as a leading force in surveillance, insurance investigations, and security services; coupled with expertise in corporate due diligence and background investigations, security consultation, litigation support, fraud, and internal investigations. Our firm has an experienced and diverse team of investigators, ranging from retired law enforcement, legal practice, and military service, available in New York, nationwide, and around the world.

You can expect nothing less than sensitivity, confidentiality, thoroughness, expertise, professionalism, and integrity in services from Radius Investigations. We take great care and pride in our cases; We do everything possible to reach a resolution to your case.

Radius Investigations helps law firms, companies, religious institutions, and individuals solve problems, advance business opportunities, mitigate risk, win or avoid lawsuits, and resolve disputes. Our services include:

  • Litigation and Pre-litigation Intelligence and Investigations- White Collar- Commercial- Matrimonial, Divorce, and Child Custody- Financial
  • Missing Person Location and Witness Interviews
  • Surveillance
  • Asset Searches and Analysis
  • Internal Corporate Investigations
  • Audit and special Committee Investigations
  • Foreign Corrupt Practices Act and anti-money Laundering Investigations and Compliance
  • Business and transactional Intelligence
  • Due Diligence and Background Checks
  • Fraud Investigations and preventative Consulting
  • Hedge Fund Investigations
  • Intellectual Property, Counterfeiting, Piracy, and Technology Investigations
  • Subpoena Compliance consulting



9/2018 PI Now: 13 Signs Your Client May Be Bugged 

Matthew D. Seifer was the featured guest writer on PI Now’s News Round-Up for September 2018. Seifer gave insight into recognizing the signs that someone may have eavesdropping devices in their home, office, or vehicle.

2/2018 Inside Edition: Put Your Cellphone to Silent and Other Tips to Help you Survive a Shooting

Radius Investigations was featured on Inside Edition on February 28th, 2018 on what to do if you are caught in an active shooter situation.

2/2018 News 12 Long Island: Run, hide, fight: seminar teachers active shooter survival skills

Matthew D. Seifer were featured on News 12’s “Nightside” on presenting an active shooter seminar to the public in response to the February 14th school shooting in Parkland, Florida.

2/2018 Are Our Children Safe On Long Island? A Roundtable Discussion

Seifer joined a roundtable discussion on the recent school shootings and what needs to be done to keep schools on Long Island safe.

6/2015 Mastic Beach hires Radius Investigations to determine why some village records are unaccounted for

(PDF of full article)

9/2016 Mastic Beach: Former official ran illegal background checks

(PDF of full article)

The Village of Mastic Beach hired Matthew Seifer to investigate how computer files and documents were stored in their offices to account for missing files. Through Seifer’s diligent and thorough investigative work, he discovered a breach in security that a former employee had illegal access to social security numbers and criminal records. The person used search engines reserved for law enforcement by posing as a police officer in the application to access the data. This former official conducted background checks on over 400 village residents, including local political figures and their families.

7/2014 Private eyes using drones to nab scammers and cheating spouses

Matthew was interviewed by the NY Post on how aerial drones can be used by private investigators, noting several cases done by Radius Investigations where having drones proved to be a game changer in gathering information. Seifer is continually building up his knowledge in utilizing the latest technology for investigations and security.



Lions Club International

Lion’s Club International is a long-standing organization that works with local communities and charities in providing service and support. Matthew has been a member since 2002 and was honored with the prestigious Outstanding Leadership and Achievement Award from the Lions Club International President. Matthew Seifer’s project work included operating as 2nd VP of Canine Companions for Independence for the Northeast region.



The CHAIN (Charity, Humility, Autonomy, Integrity, Networking) is a professional networking association that focuses on connecting with other professionals through service and charity. Matthew Seifer and Radius Investigations has worked with The CHAIN to raise money and participate with Habitat for Humanity and Bikes for Kids


Long Island Professionals On Demand

LIPOD is a network directory of professionals with expertise in their industry located on Long Island. Matthew Seifer and Radius Investigations are listed in their directory as the key experts in private investigation.


Island Business Affiliates

Radius Investigations is a member of Island Business Affiliates (IBA) as the private investigator expert in their network. IBA is a local professional network providing trusted resources for the community’s needs.

Michael Magro Foundation

Michael Magro Foundation, established in honor of Michael Magro, who lost his life to leukemia, provides awareness, advocacy, and support for families of children with cancer. Seifer participates and sponsors their annual “Evening of Tasting and Giving” event and is a member of 333 STRONG.

Long Island Networking Executives (LINE)

Long Island Networking Executives’ mission is to provide business relationships with other businesses and share knowledge from each member’s respective field. Matthew D. Seifer is the trusted representative for private investigation and security.
For more information about Radius Investigations, please feel free to contact Matthew at, or you can contact Matthew directly at 631-351-6473

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