Scott thanks for that website. Boy, was that a long description of the optical switches. They do isolate the connections from the passage of electrons from one side to another. This is called conduction. However, that is only one half of the threat to a receiver. The other half is radiation. I have attached a schematic of an ignition module. If you are not familiar with schematics, here’s a few sentence explanation. The lines represent wires or copper traces and the illustrations components. At the left side is the Hall sensor or pickup that is on your crankcase. It overhangs the prop hub that has a magnet in it. When the magnet passes by the sensor, it sends a signal that generates the high voltage that causes the spark. The spark plug is on the right side. The spark can contain radio frequency components that fall within the range that our radios work on, 2.4GigaHertz. Those components are what is called radio frequency interference, or RFI. They radiate out as an electro magnetic field just like the signal from your transmitter radiates out from its antenna. In the middle of the schematic on the bottom, you can see the “GND” terminal. That is the black wire from the ignition battery. Above that is the “Power +4.8-6V” terminal. That is the red wire from the battery. The RFI from the spark couples directly in to the ignition battery, or in this case, the kill switch with ease. The trouble with this kind of kill switch is that it is useless to stop the RFI and it couples right in to your receiver. It is easy to suppose that since a lot of guys are using these, the switches are all right. Not so. One of beauties of the 2.4 systems is that we can fly right through the interference from or fellow modelers but also through the interference that we generate in our own flight packs. So what’s wrong with that? you may ask. Plenty! You consume what is known as margin. Margin is that extra amount of a performance factor you need to make sure that you can fly safely regardless of the surrounding interference. It’s a precious value. The less margin, the more likely the system will fail. The best kill switch around is the Smart-Fly one. That optical line provides conductive and radiated isolation. Dan.