Fire alarms starting in continuous then going to code 3

I once heard a fire alarm system with SpectrAlert Classics sound where the horns sounded in continuous for about a second and then started doing code 3. Why did the horns do that?

I’ve never heard of anything like that happening so I couldn’t really tell you. I know Advances start off sounding weird on System Sensor Sync but I’ve never heard of Classics doing something similar.

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I Remember those tones since High school in St Francis MN The Wheelock AS And MTs were on Code 3 they were so loud I’m Like Jeez they are so noisy

That’s typical of most SpectrAlert signals from the classic up to now - at the initial startup there’s one long pulse followed by a normal short pulse, and then a pause and code 3 takes over. If I had to guess it’s about either waiting to capture the sync pattern from the panel, OR it’s about that first longer pulse serving as an attention-getter for building occupants.

This image is from the US patent of the MDL sync module. (Sorry its rotated weird)

My best guess is the oscillator kicking in and the devices are getting a weird signal.

i think that happens with a certain panel, but i don’t know