A leaflet published by the Maritime & Coastguard Agency (MCA) explaining the range of personal emergency radio devices that offer both Alerting Technology (typically using GMDSS) and Locating Technology (using AIS and/or GNSS)

If you fall into the sea, it may be difficult to find you, even in
moderate swell. It will be worse if no-one sees you go into the water.
So, if you fall overboard, or your boat is suddenly lost, you’ll need to
raise an alarm and ensure that you can be located. A device such as a
personal locator beacon (PLB) or a man overboard (MOB) device can
assist in your rescue.

The MCA handy guide can be printed out and kept on board – see below.