Why do arrival and departure cards exist?

Quite often it's for efficiency. Let's take the Australian arrivals card as an example, as it has quite a few questions compared with some.

Sample arrivals card for Australia

Some of the questions:

• Do you intend to live in Australia for the next 12 months?
• Do you have criminal convictions?
• Are you bringing in [food/drugs/medicine/money] into the country?

Now some of these are going to be simple 'no' answers for the most part, for most passengers. This saves customs people asking the same questions over and over again. Instead, when they see a 'yes', then they can ask. This speeds up the process for all, and more importantly, lets the customs people deal with the 'special cases' - the ones that actually matter and are what they are there for.

Do you intend to live in Australia? No = tourist. Yes = time to ask about how they support themselves, where they'll be working, etc.

Are you bringing in drugs? This one I occasionally answer yes due to the wording, as I have prescription drugs. I've sometimes been questioned on it, but usually the word 'prescription is enough'.

Now you might wonder what idiot with illegal drugs would say 'yes'. Fair enough. However sometimes the person doesn't realise their medicine from Timbuktu (random example) might be illegal or controlled substances in Australia. So it's necessary to ask to clarify, and when the person says yes, they might have a doctor prescribe them something controlled as a substitute which is allowed in the country.

Furthermore, in the event of a post-customs search of their bag, there's an additional legal benefit of asking these questions - it's made all passengers legally consider the question. And when you find drugs/food/etc in their bag, they can't say 'I didn't realise I had to declare it' - they literally just signed that they didn't have it on a form.

Now not every country has this. Some just want a place of address. I always used to be annoyed by this, especially after seeing someone use the address from Pretty Woman. Until I left my luggage at the airport (took the wrong bag), and they were able to contact me on this. While chatting to them about it (the address was the one on my bag), we were talking about the other ones and the arrival one can be used in case of emergency too. If, given the current Ebola scare, for example, a passenger on your flight was found to have it, this gives them a means to attempt to contact you to check for early symptoms and limit exposure.

So yes, they're tedious, but they do still serve a variety of purposes - for record-keeping, efficiency and legal documentation.

Entry / exit cards are partly legacy and partly legal.

Border control is a massive bureaucracy, it is very difficult to get then to change a process unless the responsible minister is an aggressive, autocratic modernizer with Darth Vader's style of office management. Yes, it would be possible to join the departure card process to the passport scan, but they keep the cards - they can't keep your passport. The joining process would cost a lot, benefit a small number of people (mostly non-tax-paying visitors) and eventually result in all the card processing people being laid off.

The other part is legal - notice you signed the card, making it a binding legal document. The 'obvious' questions that no one would answer "yes" to, like "are you carrying any prohibited items" are to cement the case against you if you do have any prohibited items. You can arrive in most countries with goods that are illegal there (but legal at your departure country) and declare them with no side effects other than possibly losing the items. If you say you don't have anything they can do you for smuggling. Scanning your passport at a self-service kiosk isn't the same.

Canada has an entry card, if you have a Canadian passport you put it straight into a scanner yourself thus automating about half the process. The computer makes the simple decisions and then rolls the dice for random inspection. But you do have to sign it first. Canada gets all their exit data from the airlines (they don't care about much when you leave. Have a nice flight, eh.