Mr Smirnov was held for two days before being releasesd
Latvia has stressed its support for free speech despite the arrest of an economist over comments he made, a spokesman for the prime minister says.
University lecturer Dmitrijs Smirnov told a newspaper the nation's currency, the lat, was heading for devaluation.
He advised people to withdraw their money from banks or change it.
Mr Smirnov was later arrested by Latvia's security police, who usually hunt for terrorists and organised criminals, before begin released.
Mr Smirnov was locked up for two days last month before he was freed. No decision has been made yet whether to charge him.
In an interview with the BBC World Service, Mr Smirnov said the police accused him of trying to destabilise Latvia's financial system.
He said: "I was scared. I am not a lawyer but I also cannot think a man can be detained for his opinion or advice in a newspaper."
Mr Smirnov, who teaches at Ventspils University College, says he was held in a cell by himself but was treated well.
The police have been reluctant to talk about the case, but in a statement to the BBC said: "The Security Police of Latvia received a complaint from a finance control institution, after that we initiated criminal procedure."
A spokesman for Latvia's prime minister said he would not comment on Mr Smirnov's arrest but said: "We support freedom of opinions, it is the base of our constitution".
Mr Smirnov says he will watch what he says in future.
Asked if he would change his advice in light of his arrest, he said: "Of course I will be more careful. I don't want again to go to prison."
He is not allowed to leave the country while the investigation continues but says there has been a "great reaction" to his arrest and he has been supported by Latvia's media.
Latvia, which has been a member of the European Union since 2004, is currently in talks with the International Monetary Fund about a possible loan.
Finance Minister Atis Slakteris has said the IMF wants the central bank to devalue the lat but the government does not want to.
The country is in recession and its output is predicted to shrink by 5% in 2009, according to the central bank.