Facial recognition returned to the latest Google Pixel phones after a short hiatus due to challenges on cost and performance, according to three former employees at the Alphabet Inc unit knowledgeable about the efforts.

The feature on the new Pixel 7 is not as good as Apple Inc’s Face ID unlocking mechanism, as it can struggle in low light and is more vulnerable to being spoofed. In addition, Google has said it is not secure enough to enable signing into apps or making payments, a Reuters report said.

The return comes after Google became stricter about launching products with facial recognition, in part due to questions about its performance on darker skin. The company took time to review its approach to training and testing facial recognition since the previous Pixel with the capability launched in 2019, one of the sources said.

Google declined to comment on several specific questions about its history with face unlock.

It said generally, “Thanks to advanced machine learning models for face recognition, Pixel 7 and Pixel 7 Pro feature Face Unlock, but we’re doing it a little differently.” It added, “We achieve good facial accuracy performance with the front-facing camera.”

Google’s pursuit of face unlock for Android smartphones spans at least a decade, but it came under greater pressure when Apple released Face ID in September 2017, the sources said.

To that point, Google struggled to devise a system that both performed quickly and was impervious to spoofing, or the use of photos or hyper-realistic costumes to fool someone else’s phone into unlocking, one of the sources said.

Engineers toyed with requiring a smile or a blink – proving a person’s “liveness” – to combat spoofing but it was awkward and slow, the source said.