Can someone explain the process for the DIY part below..

..........."Any costs will be the responsibility of home owners and
landlords. The cost of the alarms will vary according to what you
currently have in place and the alarms you choose to install We estimate
that the cost for an average three bedroom house which requires three
smoke alarms, one heat alarm and one carbon monoxide detector will be
around £220.

This is based on using the type of alarms that you can install by
yourself without the need for an electrician for installing a hard-wired
alarm".............