Very simple question, HOW MANY ET Pest Control units do I need to get rid of my Bat Control problem? It's very simple and let me tell how. The ET Pest Control units will repel around 5500 square feet (IN OPEN AREA). "THIS MEANS NOT CONFINED" to walls, doors and objects in its way. So it comes down to how bad is your problem ??? Lets say you have an attic (storage in roof top of home) and it is 80 by 40 feet in total area you need to cover (For Bat Control). If you seem to have just a few bats up in the attic then 1 ET Pest Control unit should work just great. If you have a more severe problem then 2 or 3 ET Pest Control units will definitely cure your bat problem much quicker and is your better option. Think of it this way, there are two High Impact Speakers that emit Ultrasonic Sounds from the ET Pest Control unit. The ET Pest Control units are similar to a STEREO. If you put a stereo in an open area room, you will hear the stereo at its fullest potential. But if you clutter up the room with stuff in its way, you will find your stereo to be much more muzzled and not as clear. When you add more ET Pest Control units positioned in different spots,  it's like adding more speakers to your stereo system as YOU CAN HEAR MORE INTENSE SOUNDS AROUND YOU. The ET Pest Control units are similar to stereos but are much much more intense as they serve the purpose to totally disrupting all bat control problems. In return it causes communicating problems, flying problems, eating disorders, along with totally driving them crazy with the REVOLTING SOUNDS.  Trust me NO New Bats will intrude your area once the ET Pest Control is plugged in. Again I come back to the Question How Many ET Pest Control Units do you need for your bat control problem ??? If you seem to have a light bat control problem, I would suggest placing one ET pest repeller facing toward the infested area without a lot of clutter in its way.  You will want to use more ET Pest Control units if your infestation is somewhat severe or you have a cluttered room or many rooms for that matter that have the bat infestation. Let me give you an example of what I would do if I had a bat control problem. Let's say it was in my attic and walls of my home and the bat control problem was average/severe.  First off I would do everything I could to get one unit placed up in the attic facing the most open area of the attic. (Using an extension cord can work wonders for positioning the ET Pest Control) Second of all I would place a unit in every room that I think has bats in the walls. This will ensure that I am repelling the bat control problem with the up most power along with covering every possible angle. After what I have said, your common sense should guide you regarding how many ET Pest Control units you will need and you should be well on your way for a total bat control free area.............