Alert planes

The recent article ‘Tu-160 with plasma stealth skirts hull, or something like that’ brought up the dicussion of emergency ready fighters, which got me thinking. How many nations still employ aircraft for round the clock, hot pad alert status, ready to be deployed within a few minutes notice??, as was the case with many NATO and WP air forces throughout the cold war. Additionally, out of those countries which still have emergency interceptors online, how many aircraft do they employ?, and does this amont of aircraft still provide a credible deterrence to enemy incursions of airspace in this modern age?.
P.S Also would be interested to know what kind of air defences (SAMS, EWR, etc.) that countries still have