My brother has unlocked my iPhone using his face

Young siblings can have similar facial features so it is not unusual to have a brother or sister unlock a phone. If you don’t want him to be able to access your phone, turn off facial recognition and just use a passcode.

You can't fix it.

It's very common for younger users and Face ID. Use a passcode.

Because, your brothers face was scanned at the same time as yours when you set it up. Set it up properly next time, with no one else visible.

Quoted from the OP’s reply “he was standing infront of me when I set up the Face ID”

I don't see an easy way to change this, because clearly face-id cannot distinguish your face from your brothers. as I see it, you have 2 choices from here:

1. Continue using face-id but come to terms with the fact that your brother also will have access
2. Disable Face-id and use the passcode.

If you are worried about security and do not trust technologies then please use a passcode to authenticate. Very simple.

That is not possible. Face-id only scans one person at a time. Besides, the person who is having this problem already reset their face-id. and also, even if the persons brother happened to be in the photo, they would have to be standing right in front of the camera, selfie style.

Does your brother know your passcode?

Was your brother present when you setup Face ID?

Were you present when your brother opened your phone?

You haven’t answered the questions.

Well, now you know why it unlocks using his face.

Why are you surprised when his face opens it?