Can i,v in pairs do, and else cannot work together?

This reply was getting too long to put in a comment.

So, yes you could complete this with a while true do loop. But, you'll need some factor that will break out of that loop. You'll actually be using a second thread in order to break out of the first thread.

Here is some code I wrote that should accomplish this:

local db = false
part.ClickDetector.MouseClick:Connect(function()
--Used a ClickDetector for simplicity
    if not db then
        db = true
        --wait here wasn't necessary
        while db do
			wait(0.5)
			if db == false then
				break
			end
			--added another wait here for two reasons
			-- 1. having only one wait will cause it to instantly turn off and back on
			-- 2. if you add this wait on the bottom, the second thread (user pressed f again)may not stop this loop in time
	        leftsiren.Transparency = 0
	        leftlight.Enabled = true
	        rightsiren.Transparency = 1
	       	rightlight.Enabled = false
	        wait(0.5)
			if db == false then
				break
			end
	        leftsiren.Transparency = 1
	    	leftlight.Enabled = false
	        rightsiren.Transparency = 0
	       	rightlight.Enabled = true
		end

    else
		db = false -- done immediately so the loop breaks as soon as it sees this
		wait() -- waits for loop to get finished before returning siren to original state
        leftsiren.Transparency = 1
        leftlight.Enabled = false
        rightsiren.Transparency = 1
       	rightlight.Enabled = false
        
   	end
end)

This should work as you had planned. Just change the function to your own server event function and it should do what you need it to do. Those breaks are necessary if you don't want your sirens to glitch out.