If you find a locked iPhone and Siri is still enabled, then ask Siri ‘who do you belong to?’ And she will let you know. The Settings – Siri and Search – Allow Siri when locked is what allows this to happen. And it allows other situations such as Siri reading me a message when it is locked. But maybe it is one that you consider about whether you choose to turn it on, as it may allow others to ask Siri questions. But I’ve weighed up the options, and with the added convenience for me with Siri, I have it turned on.