||We reported a wearable strain sensor, composed of a water-soluble electrode and a pH-sensitive encapsulation layer, with conforming flexibility and wear-resistance. It is enabled by the polysilsesquioxane-incorporated co-citrate elastomer that dissolves in a well-controlled manner upon pH-sensitivity. Different from the transient electronic devices, unique features of the encapsulation material give rise to exceptional operation reliability in daily life as well as selective disposability upon specific stimuli. Their organic-inorganic hybrid network structures provide enhanced surface hardness without sacrificing flexibility. The pH-sensitive dissolution behavior and mechanical properties of the co-citrate elastomer are characterized by varying the content of the polysilsesquioxane crosslinker. Finally, we demonstrate an on-demand disposable strain sensor with co-citrate elastomer that monitors fine movements of the human body and can be disposed of entirely by laundering it.