I am not a lawyer, but I can provide some general information. The legality of installing a motorcycle seat device that deploys an airbag specifically in the scenario you described can vary depending on the jurisdiction and applicable laws. It is important to consult with local authorities or a legal professional who can provide accurate and up-to-date information regarding the specific laws in your area.
In general, modifying a motorcycle in a way that affects its safety systems or operation may be subject to regulations and requirements. Governments typically have regulations in place to ensure the safety and compliance of vehicles on the road, including motorcycles. Unauthorized modifications that can potentially impact the safety of the motorcycle or the rider may not be legal.
Additionally, deploying an airbag in a controlled or intentional manner may require specific conditions or circumstances for activation, such as a collision or impact. Deploying an airbag simply based on the duration of someone sitting on the motorcycle seat, regardless of their authorization, may not align with the intended functionality and safety requirements of airbag systems.
To ensure compliance with the law and prioritize safety, it is advisable to consult with relevant legal authorities or experts who can provide guidance specific to your jurisdiction and the proposed modification you are considering.