Are you sure you have nothing to declare? Let Arnold Schwarzenegger and his pricey watch be a lesson to us all.

• Arnold Schwarzenegger was detained at Munich's airport after bringing a watch he planned to gift.
• Schwarzenegger had not declared the item, which is required by Germany's customs authority.
• A luxury travel agent says this is an important rule to keep in mind if you're traveling with gifts.

Arnold Schwarzenegger was detained for more than two hours at Germany's Munich International Airport after failing to declare a luxury watch, CNN reported.

As a result, the celebrity and former California governor will face criminal tax proceedings, Thomas Meister, a Munich customs press officer, told CNN.

"He did not declare a product," Meister told CNN. "And this process applies to everyone." Meister did not immediately respond to BI's request for comment, which was sent outside regular business hours.

According to Germany's Central Customs Authority, non-EU travelers are required to declare any goods that will remain within the country if they exceed €430, or $467 USD — in Schwarzenegger's case, a luxury watch. The traveler must also pay import duties.

"He was never asked to fill out a declaration form and he answered every question from customs officers honestly," a source close to Schwarzenegger, whose identity Business Insider confirmed, said.

While detained, Schwarzenegger agreed to pay the watch's potential taxes. This involved Schwarzenegger attempting to use a broken credit-card machine, then a failed trip to a bank, and finally, a working credit-card machine, the source told BI.

Schwarzenegger was later released from the airport and continued traveling, CNN reported.

According to the German newspaper Bild, Schwarzenegger was traveling with a unique Audemars Piguet watch. Timepieces from the brand can run up to hundreds of thousands of dollars. The same source states that the watch was planned to be auctioned off at the Austrian World Summit on Thursday in Kitzbuhel, Austria, to benefit the Schwarzenegger Climate Initiative.

"The watch will likely still be auctioned tomorrow, and the Schwarzenegger Climate Initiative will properly report it, as all of Arnold's non-profits do," the source told BI.

A luxury travel agent tells travelers to keep this in mind if you're flying with high-end gifts

Travelers arriving with items they plan to wear and keep when visiting the EU do not require declaration, Germany's Central Customs Authority's website states.

However, imported items that are intended as gifts that exceed $467 USD need to be declared, Germany's Central Customs Authority states, and travelers will need to pay an import duty fee on the item's total value.

For example, if you travel to Germany with your designer purse and bring home that same bag, you don't need to declare it. But if you pack a designer purse you plan to gift to your German friend that costs $1,500, that needs to be declared and duty fees paid.

Michael Trager, the director of the luxury travel agency TravelZork and a travel adviser at Travel Edge, told BI to keep this rule in mind when traveling with pricey gifts.

"My tip is that if you are bringing expensive gifts, you better be prepared to declare and pay taxes on these gifts," he said in an email to BI. "Personal possessions are not an issue, as long as it is obvious that they are items you are using/wearing on your journey and bringing back home."