Number of move() steps before object removes itself, -1 (default)
is never; -2 means expire when off-playfield, -3 means expire when
off-view, -4 means suspend when off-view, -5 means suspend when
off-view and expire when off-playfield.
Create timer; the timer may be one-shot (it runs only once, then
triggers the alarm and removes itself), or continuous (it continues
running and triggering the alarm)