The opportunistic networks are a subclass of delay-tolerant networks where communication opportunities (contacts) are intermittent and there is no need to establish an end-to-end link between the communication nodes. The internet of things (IoT) present the notion of large networks of connected devices, sharing data about their environments and creating a diverse ecosystem of sensors, actuators, and computing nodes. IoT networks are a departure from traditional enterprise networks in terms of their scale and consist of heterogeneous collections of resource constrained nodes that closely interact with their environment. There are different issues for these networks. One of them is the selection of IoT devices in order to carry out a task in opportunistic networks. In this work, we implement and compare two fuzzy-based systems (FBS1 and FBS2) for IoT device selection in opportunistic networks. For FBS1, we use three input parameters: IoT device storage (IDST), IoT device waiting time (IDWT) and IoT device remaining energy (IDRE). The output parameter is IoT device selection decision (IDSD). For FBS2, we consider four input parameters adding IoT device security (IDSC) as a new parameter. Comparing complexity of FBS1 and FBS2, the FBS2 is more complex than FBS1. But, the FBS2 is more flexible and makes a better selection of IoT devices than FBS1.