IEEE 802.15.4 protocol stack is the basis of many wireless sensor networks (WSN) and has been proposed for low data rate and low power applications. The standard defines a duty cycle in order to allow devices to achieve efficient energy consumption. Defining the best duty cycle configuration becomes important to extend the network life time. Several works have been done in order to study the behavior of the protocol when considering duty cycle configuration and how this configuration impacts its performance parameters. Usually, the analysis is evaluated by using simulation tools. The objective of this paper is to bring an analysis of the IEEE 802.15.4 duty cycle when considering a real scenario over TinyOS and Telosb motes instead of using a simulation approach. We show through measurement how duty cycle impacts in performance metrics such as average delay and packet drop rate in realistic scenarios.