I was in a Tesco when there was a power outage - the self checkouts all died (and rebooted into a custon Debian based OS with a Chromium front end by the looks

I was in a Tesco when there was a power outage - the self checkouts all died (and rebooted into a custon Debian based OS with a Chromium front end by the looks of it), but the staffed tills still worked and could accept Chip+PIN but not contactless.