A sensor apparatus in the form a substantially flat package for receiving and transmitting physiologic electronic signals, to be monitored or recorded, comprising in combination, a first layer consisting of hydrogel and having opposite ends, second layer sections projecting oppositely relative to the opposite ends, and consisting of hydrocolloid, a thin conductive third layer directly overlying and contacting the top of the first layer, an electrical lead in contact with the thin conductive layer, and extending to the exterior of the layers, there being phthalate-free insulation on said lead, adhesive adhering the lead to said thin conductive layer, and a cover layer extending over the first, second and third layers, and over the lead.