The most common practice is to have a physical paper form for the customers to fill out with a pen. This is a quick and economical method that doesn’t need much time and money in terms of preparation.
But it has a consequence of poor efficiency -once contact tracing is necessary, there would be a lot of manual work of organizing the data and passing it to the authority. Also, it would be hard to prevent unauthorized persons from access to personal data. Especially those restaurants asking all customers to fill their contact info on the same piece of paper. What’s worse is, the pen and paper could potentially be a carrier of virus.