A sensor having a separate antenna includes a shell, a circuit board, a nameplate, an antenna, and a connecting unit. The shell includes a substrate and a tubular wall. The tubular wall is mounted on a first surface of the substrate to form a containing space. The circuit board is mounted in the containing space. The nameplate is mounted on a second surface of the substrate which is opposite the first surface. The antenna is mounted on the nameplate and is separate from the circuit board. The connecting unit is electrically connected between the antenna and the circuit board, and is mounted through the substrate. The antenna may be mounted outside of the containing space. When the sensor is mounted on a ceiling, the ceiling may not block wireless signals, and quality of wireless communication of the antenna may be improved.