The method includes one or more turnstiles using a non-secure ranging process to detect a proximity of one or more mobile computing devices carried by respective users. The method also includes one of the turnstiles, on making a proximity determination in respect of a first of said mobile computing devices, commencing a secure authentication process to authenticate a user carrying the first mobile computing device. The method further includes, in response to a determination that the user carrying the first mobile computing device has been authenticated, allowing the user carrying the first mobile computing device to pass through the turnstile.