batteries, exposed wires and placed on infrastructure. could it be a timing device that would detonate something placed elsewhere? i don't know jack about explosives, but i think that the gimmick was reprehensible and that one cannot be cavalier about stuff randomly placed. i mean for God's sake, you can't leave a piece of luggage unattended at an airport, why would it make sense not to be suspicious of electrical devices placed on infrastructure.
Be afraid of big burly dumb men with guns.
Use your brain.
If they had placed explosives elsewhere they didn't need some electronic sign in full view to detonate it.
Explosives big - electronic detonator small.
If they managed to hide the explosives they would have hidden the detonator with it. It kind of defeats the purpose to hide the bomb and put the detonator in plain view...
Paranoia will destroy ya.