So basically have a feature that when you walk away your pc would close automatically. Windows has something like that called dynamic lock or something. Also if I am correct KDE Connect works with bluetooth now so hey, is possible: https://www.omgubuntu.co.uk/2016/08/use-bluetooth-phone-unlock-ubuntu
There are a number of bluetooth tools that do this including blueproximity and other older tools. here is another article that discusses such tools. http://www.daniloaz.com/en/automatically-lock-unlock-your-screen-by-bluetooth-device-proximity/ I Would also really like this feature.