I don't know. I imagine their accuracy runs the gamut. Heck, you can purchase a barometric altimeter in any auto supply store for a few bucks. Are they good enough to be used as triggers? I would imagine they are, but who knows?
You would think that the recently increased security would have prevented the planting of a bomb. That would seem to be especially true with respect to bombs in luggage, given the close scrutiny luggage is being subjected to.
But I wonder how tight the security is in the aircraft maintenance areas. Could a terrorist (e.g., perhaps an inside job by a mechanic who sympathizes with the radical-Muslim aims) have secretly affixed a bomb near the engine?
Still, the simplest and most explanation at this stage is garden-variety mechanical failure. We'll see.