Full wave rectified (FWR)

AC shown on top - FWR shown on bottom

Full wave rectified (FWR) is a type of power that mostly smaller/cheaper fire alarm control panels output. It's a result of AC being converted to DC without filtering. Most modern DC devices work on FWR, but other DC devices such as mechanical horns and some early electronic devices, some manufacturers first LED devices, and especially modern Simplex devices either don't work properly on FWR, will sound scratchy, or just won't work. FWR not being supported in modern devices may either be because of cost savings, or in the case of Simplex, because the panels that company makes that those devices are only installed on their panels which none of them use FWR. Smoke detectors and other system also don't work on FWR, but most panels that output FWR will still have DC filters for the Zones and 24VDC power.

Benefits

FWR panels are cheaper for the manufacturer to produce.

Cons

As mentioned some system devices especially older ones don't work well with FWR.

Bypassing FWR

FWR can be bypassed by using an external NAC/Booster panel instead of the panel's onboard NAC's.

If you have batteries in the panel, cutting AC power will force it to run on DC. While this is OK in a hobby system, its obviously not logical to do this on a real system.