This invention relates to a method of monitoring assembly of an elevator, comprising prefabricating a plurality of hoistway sections each hoistway section having a hoistway space, transporting the hoistway sections to a building site, and lifting the hoistway sections at the building site on top of each other. In order to facilitate fast and reliable assembly, a hoistway section is provided during prefabrication with a sensor device having a transmitter which is activating during prefabrication to transmit sensor data via to a data storage storing the transmitted sensor data in a memory. The sensor data is monitored, and transmission of a message to a predetermined recipient is triggered when the sensor data fulfills at least one predetermined criterion defined in an assembly plan.