We consider a scenario where multiple event-based systems use a contention resolution mechanism (CRM) to communicate with their respective controllers over a wireless network. We present a Markov model that captures the joint interactions of the event-triggering policy and the CRM. This model is obtained by decoupling interactions between the different systems in the network, drawing inspiration from Bianchi's analysis of IEEE 802.11. We present Monte-Carlo simulations that validate our model under various network configurations, and verify the accuracy of the performance analysis.