http://wccftech.com/galaxy-s9-front-fingerprint-sensor/

Despite the fabulous ‘Infinity Display’ design of the Galaxy S8, Galaxy S8+ and the Galaxy Note 8, all three devices received criticism regarding the placement of the fingerprint sensor. However, the Galaxy S9 announcement could see an end to this little gripe as Samsung has filed a patent in which a small, but accurate fingerprint sensor could be incorporated at the front-side of the upcoming flagship.

If a patent filed with Kipris, a South Korean trademarking company is to be believed, then the Galaxy S9 might feature a different design option. The fingerprint sensor could be taken from the rear side and placed at the front, with the flagship featuring a small depression at the front in order to make way for this security feature.