A downhole sub has a body defined by a wall extending in an axial direction from a first end to a second end. An inner surface of the wall defines a flow path through the downhole sub and an outer surface of the wall defines an outer diameter of the downhole sub. A compartment extends from the outer surface into the wall to having a depth less than a thickness of the wall. A housing may be removably fixed in the compartment. One or more mobile devices may be disposed in the housing. Each of the one or more mobile devices includes a sensor encapsulated in a protective material. A control element may block an opening of the housing, the control element is made of a dissolvable material configured to dissolve at a predetermined depth in a wellbore and release the one or more mobile devices into the wellbore.