Someone explain to me why this is a bad idea?

Phones studied as attack detector

By Mimi Hall, USA TODAY
WASHINGTON — The government is researching whether the best defense against a chemical, biological or radiological attack might one day be right in everyone's hands — or on their ears.

Homeland Security officials are looking into outfitting cellphones with detectors that would alert emergency responders to radiological isotopes, toxic chemicals and biological agents such as anthrax.

(snip)

Since the 9/11 attacks, the government has spent billions of dollars putting sensors along borders, at airports, in subway stations and any other crowded place that might be a terrorist target. The idea is to detect an attack as soon as it happens, evacuate people quickly and get them the antidote or medicine they would need to survive.

Basically you make it optional, maybe even with a $5-10 credit incentive**. Sensors are so advanced nowadays that it could be as innocuous as a sticker type sensor on the phone or case itself.

It's pretty obvious that no matter what you want, if the cell phone company wanted to GPS your position, they could, so use the power for good!

Am I wrong here?

**As I read further down the article, it seems that is the way it was envisioned, as voluntary.