A device, system and method for selectively activating or altering the operational mode of an autonomous in vivo device in response to in vivo conditions. They system may include an in vivo sensing device with a condition tester, and a controller. The in vivo sensing device may be in communications with an external receiver. The condition tester may include at least one layer of a dissolvable material coated on at least a portion of the autonomous device. The layer may dissolve when exposed to a specific material of a specified site along the GI tract. A sensor may be exposed when the layer dissolves or a switch autonomously activated with the layer dissolves.