Coming, ATMs that retaliate when they are attacked

, April 12: Fancy an Automated Teller Machine (

) that punches the burglar in the nose if he tries to break it open?

Well, not a punch exactly, but ATMs would soon be armed with a mechanism that would spray hot foam in the face of the attacker if he tries to force it open.

Researchers at ETH University in Zurich have developed a special film that triggers an intense reaction when destroyed.

"This could be used anywhere you find things that shouldn't be touched," said Wendelin Jan Stark, a professor at ETH's department of chemistry and applied biosciences.

Stark and his team developed a self-defending surface composed of several sandwich-like layers of plastic. If the surface is damaged, hot foam is sprayed in the face of the attacker.

The researchers used plastic films with a honeycomb structure for their self-defending surface. The hollow spaces are separately filled with two chemicals: hydrogen peroxide or manganese dioxide.

The two separate films are then stuck on top of each another. A layer of clear lacquer separates the two films filled with the different chemicals. When subjected to an impact, the interlayer is destroyed, causing the hydrogen peroxide and manganese dioxide to mix.

This triggers a violent reaction that produces water vapour, oxygen and heat. The temperature of the foam reaches 80 degrees.

The newly developed film may be particularly well suited to protecting ATMs or cash transports, said the researchers.

The number of attacks on ATMs has increased in recent years.

While protective devices that can spray robbers and banknotes already exist, these are mechanical systems, explained Stark. "A small motor is set in motion when triggered by a signal from a sensor. This requires electricity, is prone to malfunctions and is expensive."

The objective of his research group is to replace complicated control systems with cleverly designed materials.

The researchers added a dye along with DNA enveloped in nanoparticles. If the film is destroyed, both the foam and the dye are released, thereby rendering the cash useless.

The DNA nanoparticles that are also released mark the banknotes so that their path can be traced.

The findings of the study have been published in the Journal of Materials Chemistry.