The United Kingdom operates the SIS but, as it has chosen not to join the Schengen area, the UK cannot issue or access Schengen-wide alerts for refusing entry or stay into the Schengen area.
Ireland and Cyprus are not yet connected to the SIS. Ireland is carrying out preparatory activities to connect to the SIS, but, as is the case for the UK, it will not be able to issue or access Schengen-wide alerts for refusing entry or stay. Cyprus has a temporary derogation from joining the Schengen area and is not yet connected to the SIS.
https://ec.europa.eu/home-affairs/what- ... -system_en