Tripwires

Tripwires are very small amounts of troops that are sent to allied cities to see if they are under attack.

You cand send from 1 to 3 units(swordsmen, archers and hoplites) in a trip and they must be the same type of unit. 3 are the best option, because you have a good accuracy about how many troops your teammate lost. As soon the attacked city will send a report to you, if you send 3 units the report can say:

• 0 unit lost - 0-33% of the units of the supported city were lost. Or it was LS attack or trirreme attack;=.
• 1 unit lost - 33-66% of the units of the supported city were lost.
• 2 units lost - 66-99% of the units of the supported city were lost.
• 3 units lost - 100% of the units of the supported city were lost.

Knowing this, you can make a siege thread or a revolt city, if the player is offline. Or you can send a heavy support to his city depending the situation. Tripwires are very useful  and can help you to win wars, even with inactives.