Monitoring the operational efficiency of construction equipment offers great opportunities to enhance not only the productivity but also the environmental performance of construction operations. However, existing enabling technologies still suffer from a lack of economic feasibility, as well as technological compatibility with equipment fleets that are outdated or that consist of diverse manufacturers' models. In this context, this paper examines the feasibility of measuring the operational efficiency of equipment using low-cost accelerometers. Acceleration data in three axes were collected from a real-world operation of excavators that performed various duty cycles. Multiple features were calculated from acceleration data, and several classifiers using these features were tested to classify equipment operation into engine-off, idling, and working modes. An accuracy of over 93% was obtained in the classification of excavators' operation. This result has demonstrated that the application of low-cost accelerometers has the potential to provide a robust system to automatically measure the operational efficiency of construction equipment without any connection to its legacy engine system.