We present and demonstrate a new protocol for practical quantum cryptography, tailored for an implementation with weak coherent pulses to obtain a high key generation rate. The key is obtained by a simple time-of-arrival measurement on the dataline; the presence of an eavesdropper is checked by an interferometer on an additional monitoring line. The setup is experimentally simple; moreover, it is tolerant to reduced interference visibility and to photon number splitting attacks, thus featuring a high efficiency in terms of distilled secret bit per qubit.