Thank you everyone for this additional information.
As far as I can see the Hplus doesn't exist as a device. All my searches direct me to the Hplus app. That leaves me with Pebble/Mi Band/Amazfit Bip. I've looked these up but cannot see whether they are simply using the GPS for location or have additional inertial location abilities for tracking between tall buildings or under dense forest cover.
To explain where I'm coming from with this I had experience many years back with inertial navigation in the aviation field and then some years ago I bought a little Casio EX-H20G camera for documenting a field trip. The EX-H20G, despite being small and inexpensive, has a hybrid geolocation system which "stamps" each photo with the geographic coordinates of the place the photo was taken and the direction the camera was pointing. Numerous cameras and smartphones have GPS systems for location-stamping of the image files but their GPSs are of limited use because they no longer function when indoors. Casio is, as far as I know, the only one with a hybrid system which functions indoors. "Hybrid" means that it has a GPS and an inertial sensor. If you go into a building and the GPS loses its signal the inertial sensor starts tracking the position of the camera with an amazing degree of sensitivity. When I was in Milan visiting the cathedral it tracked my movements through the nave and apses so that when I took a photo of a mural it was possible to identify the mural post hoc by the position of the camera in the cathedral and the direction it was pointing. The same happened in the Galeria in Milan. However, as far as I can ascertain, smartphones and wrist trackers contain all sorts of gyroscopes and inertial sensors but only use them for sensing footsteps, screen orientation, and so forth. If I walk into a mall with my Samsung smartphone it can't track me any more and tells me the GPS is out of sight. That cheap little Casio EX-H20G with its early 2000s technology just keeps on chugging along flagging my position by inertial interpolation until it gets the GPS signal back again. And looking at its price its geolocation system must cost peanuts.
Have I got it all wrong here ? Are these fitness trackers using inertial tracking but simply calling it something else ? And are there Android apps which use the phones' inertial and gyro sensors to supplement the GPS location ?
