The　location　and　contextual　status　(indoor　or　outdoor)　is　fundamental　and　critical　information　for　upper-layer　applications,　such　as　activity　recognition　and　location-based　services　(LBS)　for　individuals.　In　addition,　optimizations　of　building　management　systems　(BMS),　such　as　the　pre-cooling　or　heating　process　of　the　air-conditioning　system　according　to　the　human　traffic　entering　or　exiting　a　building,　can　utilize　the　information,　as　well.　The　emerging　mobile　devices,　which　are　equipped　with　various　sensors,　become　a　feasible　and　flexible　platform　to　perform　indoor-outdoor　(IO)　detection.　However,　power-hungry　sensors,　such　as　GPS　and　WiFi,　should　be　used　with　caution　due　to　the　constrained　battery　storage　on　mobile　device.　We　propose　BlueDetect:　an　accurate,　fast　response　and　energy-efficient　scheme　for　IO　detection　and　seamless　LBS　running　on　the　mobile　device　based　on　the　emerging　low-power　iBeacon　technology.　By　leveraging　the　on-broad　Bluetooth　module　and　our　proposed　algorithms,　BlueDetect　provides　a　precise　IO　detection　service　that　can　turn　on/off　on-board　power-hungry　sensors　smartly　and　automatically,　optimize　their　performances　and　reduce　the　power　consumption　of　mobile　devices　simultaneously.　Moreover,　seamless　positioning　and　navigation　services　can　be　realized　by　it,　especially　in　a　semi-outdoor　environment,　which　cannot　be　achieved　by　GPS　or　an　indoor　positioning　system　(IPS)　easily.　We　prototype　BlueDetect　on　Android　mobile　devices　and　evaluate　its　performance　comprehensively.　The　experimental　results　have　validated　the　superiority　of　BlueDetect　in　terms　of　IO　detection　accuracy,　localization　accuracy　and　energy　consumption.　©　2016　by　the　authors;　licensee　MDPI,　Basel,　Switzerland.