company, said yesterday it will acquire the electronic security firm Alarmguard Holdings, Inc. for $51.4 million.

Under the agreement, a unit of Tyco will acquire Alarmguard's outstanding shares for $9.25 a share in cash. Alarmguard has 5.56 million common shares outstanding.

"Alarmguard is an excellent addition to our ADT Security business,'' Dennis Kozlowski, Tyco's chief executive officer, said.

ADT Security is the largest provider of electronic security services in the United States. Alarmguard sells burglar and fire systems and provides security monitoring services and security system repair and maintenance services to homeowners and businesses.

"In addition to securing our position in the Northeast and Mid-Atlantic states where Alarmguard has built a very strong and loyal customer base, we expect to create significant value by taking Alarmguard's local expertise in the high-end residential market and applying it to our national franchise,'' he said.

Tyco recently bought Holmes Protection and Wells Fargo Alarm.

Tyco also makes disposable medical products, plastics and adhesives as well as electronic components and underwater telecommunications systems. It does business in more than 80 countries and has expected fiscal 1999 revenues of some $17 billion.