Across America police stepped up patrols and pulled over cars as investigators searched for links between the London scare and potential plots against the U.S.

And while officials here say there is no current credible terror threat facing America, they are worried about the type of explosive device found in London could be an emerging weapon of choice for homegrown terrorists.

It's a low-tech bomb constructed out of commonly available materials: gasoline, propane, and nails.

A device that's easy to build, conceal, and transport.

And it can be triggered by a cell phone.

The information on how to make these bombs is readily available online.

Plus, there is no technology that can find them.

Unless police get a tip or get lucky in a traffic stop, gasoline bombs are virtually undetectable.

They've been used by terrorists before.

Two Lebanese students were arrested in 2006 after placing suitcases containing gasoline bombs aboard two trains in Germany.

Previous plots in Germany, New York, and the UK have all failed.

But security experts say yesterday's London scare and todays Glasgow attack send a chilling message that terrorists, whether they be Al Qaeda or homegrown cells, have embraced this easy, but deadly, new tactic.

U.S. officials say they are not raising the terror threat level, but the FBI now has sent out a nationwide alert warning police and citizens to watch for suspicious cars and be extra vigilant over the upcoming July fourth holiday.