Activating a fire alarm via battery

Well I purchased to fire alarms off of Ebay & i read the disclaimer that the fire alarms may or may not work so i used the 9 volt battery meathod and nothing, did I use the wrong cable or was the alarm dead on arrival?

I’m assuming you are referring to a notification device (horn, strobe, bell) and those are typically 24VDC. Some are 12VDC but rare. If you are only using one 9V battery, there may not be enough voltage to fire off the device. Try two 9V batteries in series to give you 18V. Still under the 24V rating but may work. I’ve been able to test 24V devices with only one 12V battery with success. Make sure you are wiring them correctly too. Horns are polarity sensitive and wiring them backwards will cause them to not function. Some fire alarm panels use that for supervision. And make sure you are using fresh 9V batteries. 9V batteries are just 6 AAAA batteries in series. If any one of those batteries are dead the whole assembly is no good.

Oh ok I’ll try that

Just so we know, what sort of alarm do you have?