To make up for the fingerprint scanner's exceedingly poor placement (Samsung told me that it is where it is because the battery prevented it from being put below the camera), the S8 has two other biometric means of unlocking the phone. The iris scanning that first debuted on the ill-fated Note 7 makes its return, and while I'm sure it's very secure, it's awkward to use, requiring me to hold the phone uncomfortably close to my face and open my eyes comically wide to trigger it.
New for the S8 is a face-scanning feature that is supposed to be the most convenient method of unlocking the phone. I say "supposed to be" because in practice, it almost never worked for me, despite being very impressive in demos before the phone's launch. More often than not, the face scanner would not see me at all, leaving me staring at the phone awkwardly, waiting for something to happen, before eventually capitulating and putting my pattern in. Samsung also says the face-scanning feature isn't as secure as the iris or fingerprint methods, so not only is it slower and less reliable to use, it's less secure, too.