A ‘Smart alarm’ system recognises attempts to break-in by detecting temperature changes and vibrations in real time

Scientists have developed a smart alarm that can set off an alarm system that recognises any attempt to break in, by detecting temperature changes or vibrations on windows in real time – leaving burglars with no chance.

The window panes of jewellery stores, art galleries and banks are protected by an alarm and fitted with security glass. However, the pane or part thereof has to break before the alarm is triggered. Conventional security glass contains metal threads that tear in the event of mechanical damage, activating the alarm.

If a cutting torch or a drill is used to damage the glass, conventional systems react either too late or not at all. Burglars exploit this weakness and use a drill or a blowtorch instead of a hammer.

Researchers at Fraunhofer-Gesellschaft in Germany developed a smart anti-burglary protection system that overcomes this problem.

The new system quickly and dynamically records thermal and mechanical stresses from external causes. Even a gentle knock against the security glass or manipulation through the use of a flame is enough to trigger the alarm.

The external force applied to the pane changes its mechanical characteristics, and the system detects this change.

This method of monitoring glass panes is based on a glass break sensor built inside an optical fibre by means of fibre Bragg grating, that is, optical interference filters inscribed in optical waveguides.

The fibre optics can be fitted in the corner of the windowpane or in other positions.

The sensor with the fibre Bragg grating is an optical sensor, which reflects a specific wavelength of light that is changed by deviations in temperature and/or elongation.

“If somebody exercises pressure on the glass pane or heats it, the distance between the grating elements changes, which in turn alters the transmitted wavelength,” said Udo Weinand, engineer at Fraunhofer Institute for Technological Trend Analysis INT.

“Sensitive optical measuring devices are capable of recording these changes. If the changes are greater than a predefined threshold, signals are transmitted to the alarm system,” said Weinand.

“We can adjust our system in a very fine-tuned, targeted manner. It can react to slight knocks and to strong ones. As a result, it can be adapted individually to the specific application,” said Peter Reinig, scientist at Fraunhofer Institute for Photonic Microsystems IPMS. The smart alarm system was rigorously tested in various attack scenarios on a wide range of different security glass panes involving hammers, baseball bats, drills, firearms, axes and heat guns to determine when the alarm is reliably triggered.

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