Why do smoke detectors go off when lightning strikes?
Lightning is a nasty thing. Powerful. Very high current at very short rise time. This causes an strong EMP (ElectroMagnetic Pulse) which will be picked up by anything conducting. A 1m free-hanging wire may create a voltage peak between its ends. Even short connections may see spikes. Decoupling doesn't always work as the EMP can enter an IC directly; it doesn't have to come by the (power) wires.
So no wonder some products experience a temporary malfunction during a lightning bolt, and high impedance mean more sensitive. If the disturbance remains within the device's voltage range it may behave wrongly without suffering damage. Higher voltage spikes may destroy (parts of) the device.  

I heard the story of a Dutch family where lightning had struck in the backyard. Every electronic product in the house was fried, from TV and PC to cameras and mobile phones. Se non è vero...  

And David with his smoke alarm network/antenna, well... :-)