I started as an apprentice with Chubb in 1976 just a few years after the take over and merger of Burgot and Rely-A-Bell. Many sites still had DC 24V signaling or gramophone record players dialing 999 and playing the message, police police police this is an automated alarm reporting from XXXX. If you fancy a laugh, I have written a series of books. Alarming Stories I, tales of an apprentice intruder alarm engineer covers the period 1976 - 1980 and can be read for free at the link below, purchased for Kobo or Kindle for £3.21 or as a paperback on Amazon - read it for free here https://www.onlinesecurityproducts.co.uk/alarming-stories.html
The second volume Alarming Stories II tales of a security engineer covers the period 1980 - 1986 and includes many photographs taken whilst I was commissioning the largest CCTV installation in Europe, the Network Southeast driver only operation CCTV system, cameras and monitors on every platform on the network. Volume 2 can be ordered on Kobo or Kindle for £3.21 or as a paperback. from Amazon.