In the ranking of annoying alarm clocks this one sure is high on the list.

The Flying Alarm Clock features a propeller-driven module, which spins off the base unit every time the shrill alarm goes off.
The noisy alarm won't turn off until you retrieve the propeller and replace it on the base.

Gadget shop Firebox sells the Flying Alarm Clock for £19.95.
Measurements of the Flying Alarm Clock are 14cm(W) x 14cm(D) x 10cm(H).