^**Note : The stated range "XXm-transmission range in open space and clear line of sight"  is the only true measurement of distance that can be given. Passing signals through Walls and other materials is not quantifiable as the composition of the material and other factors (such as moisture metal content of a wall) will affect the attenuation of the signal. The proximity to similar ambient frequencies in the location may also affect the transmission range and / or signal quality.
Digital transceivers are better at eliminating noise but still require a basic good quality signal.

Examples -

1. Plasterboard partition walls are commonly backed with Aluminium foil as a damp proofing which will block wireless signals 100%.
2. Passing through a wall obliquely can double its effective thickness and it's also not difficult unwittingly to position the console such that the signal may need to pass along the whole length of a wall (eg placed on a window sill), a situation that may sometimes give zero reception even in a room which has otherwise acceptable or good reception.
3. Some 'high-tech' glass is coated with a thin metallic film, for example to reduce solar glare, may weaken or block wireless signals, Example Car electrically heated windscreen.
4. Prevailing weather conditions. Most obviously, the range for good reception may be significantly reduced during heavy rain or hail, but might also be affected to a lesser extent in other conditions such as fog.
5. Objects around the console . This is especially true of metal or metal-coated objects, such as filing cabinets, refrigerators etc, but can even include humans. Sometimes even standing near transmitter or receiver can influence how well the signal is received.
6. Interference. Other electrical appliances can generate radio signals in the same frequency band. Sometimes this may be spill-over interference from an appliance operating on a specific nearby frequency such as a mobile or cordless phone, Internet routers. But there are also more general radiators of radio-frequency interference such as fluorescent light fittings or appliances like PCs with a plastic (or no!) case.
7. Height relationship of the aerials. The situation where the transmitter is substantially above the receiver unit (ie at a steep angle of elevation) should be avoided, because signal transmission won't be efficient in this configuration. Reception is likely to be best when both aerials are at roughly the same height, or when any angle of elevation between the two is relatively shallow. In practice, a good configuration might be for the height to be a minimum four feet, This arrangement, while by no means definitive, should help to minimise the effects of potential obstacles such as dense vegetation, people, chain-link fences.