For both attacks, I've been seeing stories of a plane, the "EC-130H Compass Call" flying in the area. It's supposedly an electronic intelligence aircraft that hasn't been seen in the sky for about a year. I don't know much more than that though

It's possible to send the trigger message on every channel.

An entire integrated explosive device + detonator + radio circuit that leeches off the host device's power supply, that you activate by blasting an area with some out-of-band signal on a frequency that propagates far and wide?

Takes some upfront work but you don't have to mess with the device, any firmware that might leave traces, and the comms network itself. You just fly a big antenna nearby and everything goes boom.

If the Israelis are as careful as they were with Stuxnet there might be a permanent kill switch baked into the implementation to prevent being triggered in the future. Without an initiating event, the type of explosive believed to be used here is very stable with respect to normal kinetic shocks or heat.