[Jotmo]

Unattended devices left by overpasses and other structures are always suspicious...

You're going to spend all day calling 911 as you move around any big city then.

and if they are found to have wires or circuitry... then they are treated as if they could be bombs.

wires=bomb. Got it. Thats some fine reasoning

As for "mass", plastic explosives take very little mass to do big damage.

If you seriously think that explosives with the mass of a circuit board and a couple of AA batteries could harm anyone if it wasn't hanging around their neck, you've been watching to much TV.

[drpix]

Got you!
Bombs are never hidden in other objects ( dolls, radios, dogs... ).
Unattended devices showing a circuit board and/or wires and/or batteries are obviously safe, so cops should ignore any 911 reports of this nature.

What world do you live in?