2#include <Misc.au3>
Local $key = True, $started = False, $hDLL = DllOpen("user32.dll")
While 1
    If _IsPressed("50", $hDLL) Then
        If $started == False Then
            $started = True
            AdlibRegister("_sendkeys", 1000)
        Else
            $started = False
            AdlibUnRegister("_sendkeys")
        EndIf
        Sleep(3)
    EndIf
WEnd
DllClose($hDLL)

Func _sendkeys()
    If $key == True Then
        Send("1")
        $key = False
    Else
        Send("2")
        $key = True
    EndIf
EndFunc