There are ways to circumvent this system, whether or not they are ethical or not – the FBI recently forced a suspect to unlock his iPhone X using Face ID. Some warrants may explicitly offer permission to use face recognition. However, many investigators will not know the alternatives and there will not always be a way to use the face of the accused. There is no guarantee that other countries will allow the detection of forced faces.
The slide also highlights the challenges face recognition poses for investigators, especially when there is no fingerprint fallback like with newer iPhones. Where it is easy to avoid accidentally triggering a fingerprint reader, you can inadvertently trigger a system such as the Face ID simply by raising or tapping the screen. Whether you like it or not, officers need to be a lot more sensitive if they want access to the latest cell phones – especially if they do not have wired access.