Rate-change/availability alerts?

Is anyone aware of a method whereby I can be alerted

(1) if rates drop at a hotel on the dates for which I already have a reservation, and/or
(2) if rooms become available at a hotel on dates for which I want to make a reservation?

Does Hilton's website offer such a service? Barring that, does any third-party website do so?

Sorry if I missed this on another thread... thanks!