I hope many people might feel little awkward to see this question. But I feel this is important. Because in my place where I am living I can get a radio (Audio Receiver) very cheaply. I don't know till what extent they allow the audio frequency ranges. I guess they use ICs for Frequency Demodulators, Frequency Clippers, etc. If the Frequency demodulator doesn't work properly and allows all the frequencies that comes through air then its going to be a big problem to the humans. Can somebody answer which are all the frequency ranges that are available and which causes human hazards?
I've learned recently that lower frequency radio waves travel farther and have better object penetration than their higher frequency counterparts.
Then you learned poorly. This is simply not correct. Different frequencies go thru different materials differently, but it is not true that lower frequencies (longer wavelengths) "travel farther" somehow.
Think of really high frequencies, like light. Here we can discern different wavelength with our bare eyes as colors. Surely you must realize that red light doesn't always "travel farther" than blue light.
What does happen is different wavelength react differently to different size objects that they can't go thru. There are three basic effects going on, reflection, absorption, and diffraction.
How much a certain material absorbs EM radiation is very material-dependent, and often not monotonic with wavelength. Think of color filters. A green filter blocks both red and blue light but lets green light thru, even though its wavelength is between red and blue.
Big things relative to the wavelength will block the radiation. However, waves also diffract along the edges of objects. This is sortof a wave bending along to follow the object. This happens only along a thin layer near the object, with the thickness of this layer proportional to the wavelength. Long waves, like 1 MHz commercial AM can bend around the edges of hills and the curvature of the earth better on a human scale than 100 MHz commercial FM, for example. This may give the impression that these longer waves "go further", but that's not what's going on.
Short wavelength don't bend around the same object as well as long wavelengths, but they can slip thru smaller holes in objects or between objects. Again, this is proportional to wavelength. A 10 m hole will easily let 3 m (100 MHz) signals thru, but mostly block 300 m (1 MHz) signals. This is probably why the shorter wavelengths work better between decks of a ship. They bounce around better and eventually make their way thru doors and the like, which longer wavelengths can't.
This is a intentional radiator. That means, in the US at least, a FCC certification number must be available on the package somewhere. Look up that number to get the details of what frequency and power the transmitter is permitted to use.
I expect there is a similar mechanism in other jurisdictions.