What happens exactly when the alerter is tripped (either push button or pedal) is you get a “penalty brake” application and the “power control” switch is tripped. A penalty brake application drains the equalizing reservoir to 0 psi at a controlled rate. The rate is controlled by the automatic brake valve. Contrast this to an “emergency brake” application which drains the equalizing reservoir to 0 psi in an instant causing a full set brake to be propagated from the head end to tail end. The power control switch when tripped disables the throttle and brings the engine to idle. To recover the engineer places the automatic brake handle to suppression/handle off, moves the throttle to idle, places the independent brake to full and centers the reverser. After about a minute the the “pc” valve resets as indicated by the pc light going out (can also hear it thump), the automatic brake can be moved to release and we are on our way. A couple of weeks ago I had an engine where the audible portion of the alerter sometimes did not work. I found this out when we stopped and I decided to stand up and stretch my legs and get a bottle of water. While stretching my legs I heard the pc valve pop then the air drain from my brake pipe. I had forgotten to center my reverser. I also had that same situation once after I had stepped out to go pee.