Saidar (pronounced: sah-ih-DAHR) is the female half of the One Power. Unlike the more violent saidin, saidar is said to be a "river of Power" which must be surrendered to or "embraced" in order to gain control.
Female channelers can tell when other women are touching the Source; a white glowing aura appears around their body, only visible to those trained to touch saidar. The ability can also be sensed in any woman capable of channeling, be they wilders or Aes Sedai. In the testing to see if you can channel, a woman channels a simple weave and waits. Within five minutes if a woman has the spark, the woman tries to channel the flow, and the test is confirmed. It takes longer for those who only can learn. However, a woman who has the spark can be detected by another female channeler without being tested.
Saidar is described as gentle, but infinitely powerful; a force which will do what you wish it to, but requires patience and submission to guide its power. Surrender is necessary to gain it, and women universally speak of it as "embracing" the Power.
There is almost no way for a woman to tell when a man is channeling, though the residues of his channeling can be detected using an appropriate weave. Lanfear shows the ability to sense male channeling up to the extent of knowing where the weaves go when fighting with Rand al'Thor by means remaining unknown. Recently an active method was discovered to discern whether or not a man was channeling or holding saidin, but this is not widely known.
A woman repeatedly channeling saidar over a longer time starts to "slow," meaning that she does not age in the same way as a woman without the ability. This also gives the woman a longer life and some have been known to live over four hundred years.
An exception from slowing are the Aes Sedai, who bind themselves using the Oath Rod, which gives them an ageless face instead of slowing the aging. The Oath Rod is also suspected to shorten an Aes Sedai's life by hundreds of years, though after being stilled, the former Aes Sedai returns to the same young appearance as she would have if she never had taken the oaths.
Another blessing received by channeling saidar is that a pregnant woman will not be sick due to her pregnancy. However, her ability to channel will be harder to control over time and the woman will feel as if her weavings are slippery and oily – fading away as she tries to make a weave.