This　study　employs　first-principles　calculations　to　investigate　the　gas　sensing　behavior　of　a　Ni-doped　indium　selenide　(InSe)　monolayer　toward　four　SF6　decomposition　products:　H2S,　SO2,　SOF2,　and　SO2F2.　Structural　optimization,　AIMD,　and　vibrational　analyses　confirm　the　thermal　stability　of　the　Ni-InSe　monolayer.　Adsorption　results　indicate　strong　chemisorption　for　H2S　and　SO2,　weak　chemisorption　for　SOF2,　and　physisorption　for　SO2F2.　Notably,　SOF2　and　SO2F2　exhibit　high　sensing　responses　(−99.5　%　and　−80.1　%)　and　rapid　recovery　times　(6.61　×　10−3　s　and　2.84　×　10−5　s)　at　room　temperature,　suggesting　excellent　reusability　and　selectivity.　Although　H2S　and　SO2　have　longer　recovery　times　at　ambient　temperature,　their　detection　becomes　effective　at　elevated　temperatures.　These　findings　highlight　the　potential　of　Ni-InSe　monolayer　as　a　stable,　sensitive,　and　selective　gas　sensor　for　monitoring　hazardous　SF6　byproducts　in　gas-insulated　switchgear　(GIS)　systems.　©　2025　Elsevier　Inc.