Developer builds Mac sleep tool that auto-recovers under battery and thermal stress

A developer has created Afterlid, a macOS utility that manages system sleep across three distinct states: normal sleep, open-lid awake, and closed-lid always-on mode. Unlike the built-in caffeinate command, Afterlid specifically handles the closed-lid scenario using a privileged helper and an undocumented macOS sleep setting. The tool automatically drops its wake assertion and restores default sleep behaviour when the battery falls below 30 percent while unplugged, thermal pressure becomes critical, or eight hours have elapsed. The developer emphasised that robust recovery logic — not just activation — is the core engineering challenge in building system utilities. Because the implementation relies on undocumented macOS internals, the developer stresses the importance of thorough hardware testing and transparent release notes.