A sensor (which could be detachable) to sense a condition (including pressure from body weight or moisture from incontinence; applied by adhering to skin of a human body or by putting a diaper on the human body, for example), a signal processing circuit, a periodic or continuous transmitter, and a power supply (typically including a battery) are associated with a flexible substrate in low profile enabling disposition adjacent the human body. A transmitter antenna is on the substrate. Insulator film between battery contacts and a switch-and-transistor combination are two power-on techniques. A bedside monitor, a transceiver configured to receive signals from and transmit signals to the bedside monitor, and a computer connected with the transceiver can be included. Other features include: notification signaling; differently responsive antennas; unique identification; low battery detection; anti-collision transmission; patient protocol scheduling; local data transfer from the bedside monitor; and out-of-range transmission detection.