Israel has ordered full military readiness by March...
They are mostly worried about Iran's Uranium enrichment capabilities....and soon their decent Russian Tor M1 9M330 Air Defense System->
They say it has the ability to shoot down aircraft as well as precision guided munitions and cruise missiles.
I would be willing to bet money that Israel will attack Iran before they can deploy those advanced air defenses.
Normally I would say Israel is posturing because Iran has it's own intelligence gathering capabilities. With the help of a Russian booster shown here Iran put up two spy sats.
Mesbah was built for Iran by Italy's Carlo Gavazzi Space. Sinah-1 was actually made in Iran. The chance an Israeli first strike could be spotted in advance is a major deterrent. However, Israel may not be alone (USA), and their threat sounds serious (they may have even asked the U.S. for aproval before making it).
(disclaimer - I am biased in favor of Israel because their culture promotes science and humanism... evidenced in that they published and spend more money on research than Iran, not to mention Iran's anti-humanism government)