Background process for mobile device tracking web site

I am working on a web site for emergency service workers that would also track the position of each person from thier Mobile phone with thier permission when they log on. I am able to open a web page and using JS and PHP write away the coordinates of the user to a mysql database then display the result on a google map using API The problem is that I need to run the saving of the coordinates in the background, as if the user moves to a new page and loses focus of the page writing the data or auto lock kicks in on the mobile (ie goes to sleep) the writing of the data stops I have tried working with 'web workers', but they seem to NOT allow PHP code so I cannot write away the coordinates to MySQL Any suggestions for how I might be able to run a background process that writes the data to MYSQL even when focus is lost or device goes to auto-lock, I can stop the process when a close indicator is made in the database stopping the incident tracking so it does not run for ever Any ideas most welcome