Since 1996, the Federal Communications Commission (FCC) has set regulations and guidelines on all wireless communications devices sold in the United States. The wireless products must meet minimum guidelines for safe human exposure to radio frequency energy. The limits established in the guidelines are designed to protect the public health with a very large margin of safety.
The Specific Absorption Rate (SAR) is a measure of the rate at which energy is absorbed by the human body when exposed to radio frequency (RF) energy. The general population exposure limits set by the FCC for the frequency range that is utilized by smart meters and other devices like cordless phones and baby monitors, is 0.6 milliWatts per centimeter squared (mW/cm2) at 902 MHz and 1.0 mW/cm2 at 2.4 GHz. Products used within 20cm of the human body must undergo SAR testing to ensure that the rate is below the limits
The FCC has outlined exclusions where the power is low enough that SAR testing is not warranted. In Knowledge Database (KDB) article 447498 this is outlined as:
[(max power of channel, including tune-up tolerance, mW)/(min test separation distance, mm)]*[√f(GHz)] ≤ 3.0 for 1-g SAR and ≤ 7.5 for 10-g extremity SAR.
As an example, use the LR Series at 433.92MHz. The maximum output power that the module is capable of is a little under 10mW. Assume a separation of 5mm as a reasonable separation distance through an enclosure.  The calculation is:
(10mW / 5mm) * (√0.43392GHz) = 1.3
This is less than 3.0 and would be excluded from SAR testing.