Being in the stage machinery business, I have never relied on something like a wireless smartphone for a deadman switch. You need certified hardware&#x2F;sofware meeting relevant standards.<p>This is why I still use industrial PLCs for my installations over my Pic chip or Arduino creations. I will use them in non-safety related, temporary installations, but unless I have had the HW&#x2F;SW third-party inspected, I&#x27;ll stay with the certified combination. An industrial e-stop relay is more than just certified compared to a 5V relay you typically use with an Arduino or Pic chip project to control motors, or other actuators.<p>There are protocols, and there can be rules, such if WiFi signal is lost, e-stop, but I have personally tested such a system where the hydraulic lift continued to run when WiFi was lost even with a rule to prevent it. Good thing I was standing purposefully near a hard-wired e-stop.