Various studies have shown that 40% or more of smart phone users do not use any authentication mechanism on their devices and most of the users cite “inconvenience” as the reason. [1,2].
The “Age Group” – “Current Authentication Scheme” distribution. 
This entails that the usability issues of current authentication methods, has left a large proportion of smartphone users unprotected and in risk of data theft.
Continuous Authentication (CA) has been proposed as a method of addressing the usability issues of current smartphone authentication methods. CA uses behavioural biometrics to continuously and transparently authenticate the user. Some examples of behavioural biometrics:
- The way users touch or swipe the screen
- The way users walk (gait patterns)
- Facial attributes
- Voice charachteristics
But while the idea of CA has been around for more than 10 years, none of the proposed CA schemes has seen a widespread implementation on one of the main mobile platforms.
This research aims at a comprehensive evaluation of proposed CA schemes to find the main issues hindering their widespread implementation :
- First a comprehensive set of evaluation criteria is presented.
- Then the proposed CA schemes are evaluated based on those criteria to find the main adoption issues.
 S. Egelman, S. Jain, R. S. Portnoff, K. Liao, S. Consolvo, and D. Wagner. Are you ready to lock? In ACM SIGSAC Conference on Computer & Communications Security. ACM, 2014.
 M. Harbach, E. von Zezschwitz, A. Fichtner, A. De Luca, and M. Smith. It’s a hard lock life: A field study of smartphone (un) locking behavior and risk perception. In Symposium on Usable Privacy and Security, 2014.
 H. Khan, U. Hengartner, and D. Vogel. Usability and security perceptions of implicit authentication: convenient, secure, sometimes annoying. In the proceedings of the 11th Symposium on Usable Privacy and Security (SOUPS), 2015.