This paper presents PAS-MAC, an asynchronous anycast medium access control protocol for IoT. A low-power ad hoc wireless network acts on the data collection side of the IoT, measuring environmental variables and transmitting them, by multi hop, to an edge computer. PAS-MAC is a duty-cycled protocol based on Low Power Listening (LPL) method. Differently from other asynchronous MAC protocols, PAS-MAC probes the channel to identify activity over a very short interval, reducing the network energy consumption when no message traffic is present. In order to establish communication between two nodes, this protocol sends a series of short preambles containing information to find a forwarder for data message, which is elected among some good forwarding candidates. Data communication process is split in two phases: asynchronous and synchronous. In the first one, preambles are sent in advance to determine the route and synchronize the forwarding nodes, in a staggered manner. In the second phase, data is sent synchronously in a pipelined fashion. While anycast communication pattern reduces the end-to-end latency, short probing (from LPL) reduces the energy spent by the network. Simulation results show that PAS-MAC achieved, for the majority of tested scenarios, a combination of small end-to-end latency and low energy consumption in idle mode. No other tested protocol had similar performance in these two areas at the same time.