It is quite common to associate the term 'security device' with burglar alarms of various types but in fact, any piece of equipment which helps to protect people or property could correctly be termed a "security device". Therefore this book is not solely concerned with burglar alarm systems, and includes other types of circuit such as a gas/smoke detector, flood alarm, fire alarm, and a doorphone/baby alarm.

A substantial part of the book is used to cover burglar alarms and details of simple switch activated circuits are provided, as well as some more sophisticated circuits using light, infra-red, and ultrasonics.

As most of the circuits are fairly simple, and suitable strip-board layouts are provided, construction of the various devices should be well within the grasp of the average electronics constructor, and in most cases will not be beyond the capabilities of the beginner.