September 2008 Tech Talk Online Q & A


Q: I have been heard that one should be careful at replacing standard Alkaline 9 volt batteries in smoke detectors with 9-volt Lithium batteries. To me it would seem that the Lithium battery would last a longer time so what is the problem?

A: Yes, you typically do get longer time with a Lithium battery. The caution is that a Lithium battery discharges at a different rate as an Alkaline battery and my not work with the typical 30 day low battery warning circuit of the smoke detector. While Alkaline batteries have a long, slow low battery decay, Lithium batteries keep a high voltage longer but drop more quickly near the end of the batteries life. Customers should be made aware that if they get a smoke detector’s low battery warning with a Lithium battery they should change it right away. It is always recommend that you check with the smoke detector manufacturer to find their recommendations on Lithium batteries.

Q: Recently I was working with some access control equipment that required a serial RS-232 connection with a PC computer. There was some trouble with the serial communications and it was thought that the serial port of the computer was bad. Is there a quick an easy way to test just he serial port (COMM(X)) of a computer?


An old trick for testing a computer’s communication port is the use of a simple improvised hardware device call a loop-back plug. The two key pins in a RS-232 connector pins three and two, which are for signal receive and transmit respectively. If you short out these pins you are basically sending a transmitted signal back into the comm port receive, thereby testing the port. This can be done simply with a paper clip on a female DB-9 or a spare motherboard jumper on a male DB-9. You will need to use something like Microsoft Hyper-Terminal program to send test data to the port. Hint: If you have Echo on you will see double letters in this test.


If you enjoyed this article and want to receive more valuable industry content like this, click here to sign up for our FREE digital newsletters!

Security Is Our Business, Too

For professionals who recommend, buy and install all types of electronic security equipment, a free subscription to Commercial Integrator + Security Sales & Integration is like having a consultant on call. You’ll find an ideal balance of technology and business coverage, with installation tips and techniques for products and updates on how to add to your bottom line.

A FREE subscription to the top resource for security and integration industry will prove to be invaluable.

Subscribe Today!

Get Our Newsletters