Terms of the transaction were not disclosed.
SDI specializes in public safety and homeland security solutions. I-sys provides integrated security management systems, end-to end building automation, mechanical services, and advanced fire safety systems.
Among i-sys clients are airports, seaports and banking institutions.
"I am incredibly proud of what the i-sys team has achieved, and look forward to blending our technical talent and experience with SDI to bring further innovation to the security market," i-sys Chief Executive Officer Debra Ohlendorf said. "SDI shares our extraordinary focus on customer satisfaction and retention, and will be a great partner for both our team and our clients."
Added SDI founder and chief executive officer David A. Gupta: "SDI addresses the complex information systems and operational processes that are at the core of today's advanced safety and security technologies -- from smart devices to analytical software.
"The i-sys team's deep technical expertise and national service network further position SDI to deliver unbiased strategic advice and operational support for these integrated, multi-layered systems."