One of the most challenging and yet most rewarding parts of alarm systems is in the area of life safety. Most of the time when life safety is mentioned we think of fire alarm systems; however, another area is the application of robbery, duress and hold-up alarms (HUAs).

The proper installation and operation of HUA systems is critical. During a hold-up there is always a high possibility that the loss of human life is imminent. A store employee may be shot by the robber and only have moments to summon lifesaving help. Performance of the users, sensors and communications must be precise and without error.

Dealers and technicians must be aware of this responsibility all the way from the proposal stage through to the final tests and commissioning of the equipment. Did you install a HUA device that the customer can get to quickly and easily, and that it will work flawlessly?

Design, Practices Cut False Alarms

If the technical demand for precise performance of HUA systems was not challenging enough, the additional pressure for zero false alarms by police departments is paramount. Typically, a HUA system is silent so as not to panic the robber and dispatch is immediate with very little opportunity for false alarm verification. Police arrive with shotguns drawn and have very little patience for even a single false alarm.

I remember the time I visited a convenience store that was part of a large national chain. I was doing an audit of the customer’s alarm system and asked to see their wireless HUA button devices. The representative stated, “That’s easy, they are all here in my office drawer.” I commented how ineffective this was and he mentioned he had a problem with employees accidentally tripping them all the time. When I asked if he regularly had HUA drills he said they did not.

 What could have helped this manager? Most HUA equipment manufacturers now provide HUA buttons that are recessed or have raised bump guard rings to prevent accidental button depression. One of the best solutions is a double-button configuration in which both buttons have to be pressed simultaneously for a valid alarm.

I personally prefer latching or locking double-button HUA devices. Some are mechanically latching and require a small key to release. Other devices have an electronically latching LED indicator (see Tool Tip) in which the power must be reset. Since HUA sensors are closely grouped in a facility it is not uncommon for many to be in the same alarm loop. Latching devices makes the employee stationed at a particular location more accountable for an accidentally tripped HUA device.

Building the Perfect Bill Trap

One of the most challenging HUA applications is the use of currency bill sensors or bill traps. The cash drawer is a very busy area and the use of these sensors can create false alarm problems. A while back the Central Station Alarm Association (CSAA) provided the industry with alarm performance guidelines STA-1 (www.csaaul.org/CSAASTA1.htm). Following is an excerpt from the section dealing with bill traps.

“In instances where bill traps are to be used, they should be installed in pairs so that both devices must be activated before a hold-up alarm signal is transmitted to the monitoring facility. When such an arrangement is provided, a trouble signal should be sent to the monitoring facility if only one bill trap is activated so that the situation can be corrected without delay.

“As an alternative to a trouble signal to the monitoring facility, or where the hold-up alarm is monitored by a police department directly, a local trouble indicator may be used. The local trouble indicator shall not be visible or audible to the potential criminal.”

Note the reference to creating a logical “and” by requiring two sensors for an alarm. Also note the suggestion to have either single sensor activation create a trouble. Many new CP01-rated alarm panels allow for this to be accomplished in cross-zone programming. However, what about retrofitting this configuration in older panels?

For situations with older panels or when only a single zone is available you may want to refer to the diagram in which you will find the Dolph Double Trap (DDT) configuration (yes, named after yours truly) to help comply with the CSAA STA-1 bill trap guidelines. Most bill trap sensors come with a single pole double throw (SPDT) or 1 Form C switch configuration, and this circuit diagram takes advantage of this.

The normally closed (NC) switch position indicates when money is in the bill trap sensor. You may pair more than one set of sensors in parallel with the end of line (EOL) resistor behind the last pair of bill trap sensors. If you would like further suggestions and a circuit diagram on how to use the DDT circuit with local LED trouble annunciation,  visit my Tech Shack blog.

Be sure to check out the many types of wireless bill trap alarm devices as they are easy to use in cash drawers that are constantly moved around. Some now come with local LED indicators and alarm transmission delays in case money is accidentally removed. If you want to additionally apply the DDT circuit for two wireless bill trap units you can wire it directly to the relay contact output of the wireless receiver.

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