A tornado siren cannot be sold like a private good because the supplier cannot:

1. Selling something requires being able to withhold it. 2. Radio stations, tornado sirens, light houses, and street lights are all nonrivalrous and nonexclusionary. 3. Nonexclusionary means everyone within earshot hears the siren whether they paid or not. 4. That is why such goods are typically funded publicly rather than sold. 5. Building more sirens is perfectly possible; the problem is charging for the first one. _Source: OpenStax Principles of Microeconomics for AP(R) Courses 2e (CC BY 4.0), Ch 13 'Positive Externalities and Public Goods', sections 13.1-13.4_