Can two 433MHz based systems co-exist?

It is possible for two 433MHz based systems to co-exist in the same environment? Or does the mere fact that they share the same frequency space make it not practical?

Yes they can exist ...provided they use orthogonal polarization...I mean differnt polarization...and all other system components mainly the Antennas are subjected to detect the same...

Antenna polarisation does not work in in-door or enviroments with lost of objects since lost of different reflections will be created all polarized differently. And even if it would work the difference is only some 3 dB. If your system(s) does not use 100% duty cycle but far less its no problem at all !.

OKay..but why the difference between two polarised components is 3dB only...?
I really didn't know that polarisation thing dosen't work in indor...but to counter...if we can maintain the difference 6db or above ..we can use same frequencies in indoor...which may or maynot be possible..

Indoor will change the polarisation after reflection and if you have an enviroment with lost of reflections (indoor) you will have no polarisation anymore... Most antenna's have some 3dB between V and H planes, check antenna books and lit. Also plarisation works best far outside the Fresnell zone and not 10 cm or 1 meter away from the antenna at 433 MHz !