These are more important for some investigations than others, the larger the site under investigation and the more spread out the teams the more essential good two-way communication becomes. 

Some see this as a nuisance, mainly due to the sudden interruptions that can occur, ic can also make you jump, while others see this as a positive asset especially when you need to ask, "was that you that slammed the door".

Look for radios that have at least a claimed 2-mile range, at least 8 channels and a good number of side bands, 38 is ideal, 20 will do. If 2 miles sounds a long range a careful read of the manufacturers manual will quickly reveal that the quoted range is line of site outdoors, no trees or anything in the way. Indoors in a rambling building or near hills the range will drop very considerably.

An example of our Cobra two-way radios that the tech team use is shown below, these are rechargeable but take normal batteries when required. These have a good range indoors in an old large building with thick walls and between half and 2.4 miles outdoors, depending upon the terrain.
 

For reasons of economy rechargeable units are always best, but make sure that you have the option to use AA or AAA cells should the rechargeable cells get discharged and you need the units back in action quickly. Remember that some haunted locations can discharge batteries very rapidly, spare batteries stored away somewhere are a sensible precaution.

A similar set to these were used a while back at Michelham Priory and were capable of working through the thick walls of the main building and gatehouse as well as covering the distance between the two with ease.

One good tip is that If you need more that one pair of units always buy the number of sets that you need at the same time and of the same type if at all possible. Although that said, it is often possible to mix and match as we have done, but more care is needed. If possible trying out your current sets with the ones you are buying before parting with your money is a good idea it is not always possible. Although our other units were bought separately, they work absolutely fine together and we have found that when we are working with other groups problems are not that common.

It takes quite a while to set up four or more units and to test them, make sure you do this well before you need to use them and of course make sure you know how to use them (preferably in complete darkness) and are ready and able to impart this information to the other team members reliably and quickly, you don’t want to miss out on something when it starts happening just because your radio is on a different frequency. Another good thing to look out for, our sets can have the frequency change keys locked when in use, it is wise to make sure that the lock is applied its easy to change the channel by accident when fumbling around in the dark.

One small point, the frequencies used by two way radios are in the 2.4 GHz band. If you are using a wireless router or are using DVR cameras be aware that radios can interfere with them if they re on the same or an adjacent channel. Most DVR cameras work on channels 1 to 4 so keep your radios above channel 6 for safety. If you are using a wireless router or wireless access points use channels 11 to 13. That way all will happily have a good chance of co-existing.