Alderney is probably one of the safest destinations you can visit. Crime is rare and the little crime is fairly minor. People generally leave doors unlocked and often leave vehicles unsecured with the keys in the ignition. However, do not emulate the locals in this regard. If you have a hire car and it is 'borrowed', you will find you will not be insured when it is discovered in a damaged state on one of the unmade roads having been used to get to a German bunker for an after-hours party. This seems to happen to at least one unlucky local every year. Every summer, the police remind people to lock cars and remove their keys for that reason.
Public order offences are not as rare as the locals would have you believe. Unlike the UK, which has liberalised its drinking laws, Alderney observes strict licensing hours, which, although fomerly the longest in the British Isles, are now probably the shortest. In the winter, no alcohol may be served after midnight, and all premises must close by 12.30. In the summer, these hours are extended by half-an-hour.
Alderney, like the UK, Ireland, Jersey and Guernsey, has now banned smoking in public places. Sark remains the only Channel Island with a pub where smoking is permitted.