The System Sensor SPWL is a white, wall-mountable, high fidelity speaker for indoor use. It's part of the System Sensor L-Series, which includes speakers and speaker strobes. The SPWL has a frequency range of 400 to 4000 Hz and a power range of 1⁄4, 1⁄2, 1, and 2 watts. It can be used with a nominal voltage of 25 volts or 70.7 volts.