Is it possible to unlock someone’s iPhone with your Face ID?

Yes, it is possible Face ID can work with other person and statistically for siblings those odds are higher.

About Face ID advanced technology

The probability that a random person in the population could look at your iPhone or iPad Pro and unlock it using Face ID is approximately 1 in 1,000,000 with a single enrolled appearance. As an additional protection, Face ID allows only five unsuccessful match attempts before a passcode is required. The statistical probability is different for twins and siblings that look like you and among children under the age of 13, because their distinct facial features may not have fully developed. If you're concerned about this, we recommend using a passcode to authenticate.

Hello ~ Take a look here and pay close attention to excerpt:

About Face ID advanced technology - Apple Support*

*The probability that a random person in the population could look at your iPhone or iPad Pro and unlock it using Face ID is approximately 1 in 1,000,000 with a single enrolled appearance. As an additional protection, Face ID allows only five unsuccessful match attempts before a passcode is required. The statistical probability is different for twins and siblings that look like you and among children under the age of 13, because their distinct facial features may not have fully developed. If you're concerned about this, we recommend using a passcode to authenticate.

~Katana-San~

iW00 wrote:

Yes, it is possible Face ID can work with other person and statistically for siblings those odds are higher.

Ah, OK. I'm sorry.

I have my doubts about Face ID and don't use here on my iDevices.

But really didn't expect that's possible for a random person to be able to unlock an iDevice secured with Face ID.

A passcode seems safer . . . . .

Raicya wrote:

A passcode seems safer . . . . .

Chances someone can see the passcode you use to unlock your iPhone and remember it are higher than some random person unlocking your iPhone using Face ID.

But your iPhone and your rules how you want to use it…

Hello ~ It is “possible” but highly unlikely. I feel safer using the Face ID because my 9 year old granddaughter watched me unlock my iPhone with my passcode ( I wasn’t aware she was watching me.) and had access to my device…for a very short period of time :)

~Katana-San~

NO.

Does your sister know your passcode?

Were you present in the room when your sister unlocked your phone?

Was your sister present when you established Face ID?