Okay, this is a tricky situation. You're right to be cautious about relying solely on ChatGPT for code compliance. Here's a breakdown of the issues and my thoughts, along with what I would consider the best practice.

Issues at Hand



Mechanical Integrity

Directly mounting a sounder base (especially one containing electronics) directly to drywall, without proper support, is almost certainly going to lead to problems. Over time:

Vibration

The sounder itself creates vibration. This will loosen the mounting screws and potentially damage the drywall around the holes.

Weight

While the sounder base isn't incredibly heavy, the constant pull of the wiring and the weight of the device itself will stress the drywall.

Installation/Maintenance Damage

Someone will inevitably push too hard on the base during installation, testing, or maintenance, causing further damage.

Code Compliance (The Gray Area)

NEC is not black and white. You're right; the NEC doesn't specifically say, "Thou shalt not mount sounder bases directly to drywall." However, it focuses on secure support.

NEC 300.11 (A)

"...wiring methods shall be adequately supported and secured...". This is a key section that is violated. The Code requires the wiring method to be supported. The wiring in this case is the wiring leading to the smoke detector.

Why It's a Bad Idea (Beyond Code)



Reliability

Loose connections, damaged wiring, and eventual failure are all more likely.

Professionalism

It simply looks unprofessional and indicates a lack of attention to detail.

Future Problems

Makes future maintenance and troubleshooting more difficult.

Acceptable Solutions1. Use the Properly Sized Box

This is the best option. Remove the single gang cut-in boxes and install the four-square boxes required for the device. This is the best way to ensure proper support, wiring space, and compliance.2.

If no box, then a bracket

There are specific brackets that can be used to secure the device to the drywall if a box isn't an option.

Recommendation


Talk to the Authority Having Jurisdiction (AHJ)

This is the most crucial step. Discuss the situation with the local building inspector or fire marshal. Get their opinion on whether they will approve the installation using method 2 or if they will require a full four-square box.2.

Correct it Now

If possible, correct the situation. Remove the single-gang boxes and install four-square boxes. It's easier to do it right the first time than to deal with call-backs and potential liability later.

In summary: Mounting directly to drywall might technically skirt a direct code violation in some interpretations, but it's poor workmanship, creates long-term reliability issues, and reflects poorly on the installation. Do it right the first time with proper support. Flag for review