Appurtenances to wound dressings can include: a substrate configured to attach to a wound dressing; a fluid-activated voltaic cell attached to the substrate; a transmission unit attached to a surface of the substrate, the transmission unit including circuitry and at least one antenna, the transmission unit configured to transmit a signal in response to current generated by the fluid-activated voltaic cell; and a projection operably attached to the fluid-activated voltaic cell, the projection of a size and shape to extend into an interior region of the wound dressing and configured to sample a fluid within the interior region of the wound dressing.