Despite the increasing usage of mobile communications, strengthened by the growing penetration of smartphones, end users seem to be concerned about the potential health risks of the electromagnetic fields (EMF) induced by such technologies, according to the latest statistics gathered by the Eurobarometer. The Low EMF Exposure Networks (LEXNET) project aims at designing techniques able to reduce the corresponding exposure, without jeopardizing the quality of experience perceived by the end-users. In order to tackle that goal, a first step must be to accurately estimate such exposure, even in large areas, and with real operating networks. This paper introduces the work that is being carried out to deploy a number of low-complexity dosimeters to characterize the EMF at four different bands. The devices exploit the facilities provided by a wireless sensor network testbed, and are therefore integrated as another IoT (Internet of Things) node. The preliminary measurements that are discussed in the paper assess the validity and feasibility of this novel methodology, which provides clear advantages to other traditional procedures, such as the use of drive tests and/or spectrum analyzers.