In the US Navy, there are five:
Condition I - General Quarters, all hands at battle stations
Condition II - Modified General Quarters, used in large ships to permit some relaxation among personnel
Condition III - Wartime Cruising, generally one third of the crew is on watch, and strategic stations are manned or partly manned. (e.g. weapons)
Condition IV - Optimum Peacetime Cruising, provides adequate watch manning, provides personnel economy. It is normal peacetime cruising condition.
Condition V - Not normally a condition, IN-PORT ROUTINE.
Not alerts but material conditions of readiness, i.e, increased level of water-tightness, with X-RAY being the least and ZEBRA the most. Each watertight door and hatch is labeled X, Y or Z and are required to be dogged closed if that level of readiness is set.
X-RAY allows YOKE and ZEBRA to be open, YOKE allows only ZEBRA to be open and ZEBRA requires all to be closed. Regardless of material condition, a log is kept in the Damage Control Office on whether a hatch or door is dogged open or close.
ETA: Material conditions of readiness are tied to the 'alerts' above but can also be set in other circumstances, such as UNREP ops, high-traffic areas or bad weather.