This book constitutes the refereed post-conference proceedings of the Fourth IFIP International Cross-Domain Conference on Internet of Things, IFIPIoT 2021, held virtually in November 2021.

The 15 full papers presented were carefully reviewed and selected from 33 submissions. Also included is a summary of two panel sessions held at the conference. The papers are organized in the following topical sections: challenges in IoT Applications and Research, Modernizing Agricultural Practice Using IoT, Cyber-physical IoT systems in Wildfire Context, IoT for Smart Health, Security, Methods.

Inhalt
Challenges in IoT Applications and Research.- Challenges in IoT Applications and Research.- Modernizing Agricultural Practice Using IoT .- sFarm: A Distributed Ledger based Remote Crop Monitoring System for Smart Farming.- Smart Agriculture using Flapping-Wing Micro Aerial Vehicles (FWMAVs).- Smart Lysimeter with Crop and Environment Monitoring: Enhanced with Pest and Crop Control.- Cyber-physical IoT Systems in Wildfire Context.- Fuel break Monitoring with Sentinel-2 Imagery and GEDI validation.- A Study on Small Sensor Node Antenna Performance Camouflaged under Grassland Fire.- A Data Fusion of IoT Sensor Networks for Decision Support in Forest Fire Suppression.- Drones as Sound Sensors for Energy-Based Acoustic Tracking on Wildre Environments.- IoT for Smart Health.- cStick: A Calm Stick for Fall Prediction, Detection and Control in the IoMT Framework.- Hardware/Software Co-Design of a Low-Power IoT Fall Detection Device.- Security.- ReOPUF: Relaxation Oscillator Physical Unclonable Function for Reliable Key Generation in IoT Security.- Cyber-Physical Application for the Safety and Security Enforcement in Oil & Gas Transportation.- A Secure and Efficient Cloud-Connected Body Sensor Network Platform.- Methods.- EasyDeep: An IoT Friendly Robust Detection Method for GAN Generated Deepfake Images in Social Media.- A Fuzzy Logic Approach for Self-Managing Energy Efficiency in IoT Nodes.- Hydric Resources and Metereological Monitoring IoT System - The Software Architecture.