Rules and regulation on what should be SAR value of a mobile?

Every mobile phone model is tested for radio wave emissions. A measurement is made using an internationally agreed method that meets government and regulatory standards. This gives the mobile SAR value, which must be below an agreed level of SAR value of mobile. Only mobile phones that pass this test are allowed to go on sale.Mobile having SAR value more than agreed level can't be sold.

why SAR value of a mobile is necessary?
Your mobile device is a radio transmitter and receiver. It is designed not to exceed the limits for exposure to radio waves recommended by international guidelines. These guidelines were developed by the independent scientific organization ICNIRP and include safety margins designed to assure the protection of all persons, regardless of age and health.
Guide lines on SAR value of a mobile.
The exposure guidelines for mobile devices employ a unit of measurement known as the Specific Absorption Rate or SAR. The SAR limit stated in the ICNIRP guidelines is 2.0 watts/kilogram (W/kg) averaged over ten grams of tissue. Tests for SAR are conducted using standard operating positions with the device transmitting at its highest certified power level in all tested frequency bands. The actual SAR level of an operating device can be below the maximum value because the device is designed to use only the power required to reach the network. That amount changes depending on a number of factors such as how close you are to a network base station.
The highest SAR value of a mobile

under the ICNIRP guidelines for use of the device at the ear is 1.10 W/kg
Use of device accessories and enhancements may result in different SAR values. SAR values may vary depending on national reporting and testing requirements and the network band