How do I check an alarm company is genuinely approved?

Look the company up on the NSI or SSAIB register directly, on the inspectorate's own website, using the exact legal entity name and company number from the quote — not the trading name and not the logo on the website. Confirm the certificate is current and that its scope covers the service you are buying.

Logos are trivially copied, and expired certification does not remove them from a website. The register is the only check that means anything, and it takes about a minute.

Do this specifically:

Get the legal entity name and Companies House number from the written quote. Search the NSI and SSAIB registers for that entity. Confirm the certificate is in date, and read its scope — intruder alarms, CCTV, keyholding and fire are separately certificated. If the quote comes from a different entity than the one on the register, ask why in writing.

Then check the ARC separately. Your installer may be approved while subcontracting monitoring to a centre you have not been told about. Ask which ARC will monitor the system and confirm that centre's own certification.

Finally, check Companies House for the entity itself: incorporation date, filing history, and whether it is the same company that has been trading under that brand. A brand with a long history and a company incorporated last year is worth a question.