I'm building a DIY security system for my home, but I'm using the existing sensors and siren that are already installed from my old security company.
So, I don't know the current draw of the siren or have a part number for it to look up the datasheet, but I'm attempting to make sure I have a sufficient transistor/relay to switch it on. All I know is that the siren is 12V (from measuring the alarm output of the previous system with a multimeter).
Is there a way I can measure the current draw of the siren without actually sending current into it? It blares at around 105dB, so I'd love to try to figure out a way to determine this without the deafening tone or attracting the attention of my neighbors.
I considered measuring the resistance of the siren, since it's probably just a piezo, and using Ohm's law, but I'm not sure that would give an accurate estimate without knowing what kind of other driving circuit, etc. is inside the siren.