The use of AE for testing the integrity of structures has a long history but its use for continuous monitoring of structures is not so well established. In a world of ageing infrastructure the need for methods of continuous monitoring is increasing so that the operation, maintenance and repair of structures can be more effectively managed. The extent to which AE will play a role in this obviously depends upon how effective it is in providing the wanted information in a timely manner to those who need it. However, other crucial aspects in its adoption will be the ease with which it can be used (e.g. specified, installed, interpreted) as well as its reliability and lifetime costs. With these considerations in mind, a multi-channel monitoring system has been developed called SIMPALTM. Throughout its development, field trials have been conducted with the aim of exploring the practical usefulness of a simpler kind of AE system. This paper provides an overview of the approach taken in developing the system and presents data gathered during proving trials and from its practical application to structures such as bridges.