Since last week, Saudi women's male guardians began receiving text messages on their phones informing them when women under their custody leave the country, even if they are travelling together.

Manal al-Sherif, who became the symbol of a campaign launched last year urging Saudi women to defy a driving ban, began spreading the information on Twitter, after she was alerted by a couple.

The husband, who was travelling with his wife, received a text message from the immigration authorities informing him that his wife had left the international airport in Riyadh.

"The authorities are using technology to monitor women," said columnist Badriya al-Bishr, who criticised the "state of slavery under which women are held" in the ultra-conservative kingdom.

Women are not allowed to leave the kingdom without permission from their male guardian, who must give his consent by signing what is known as the "yellow sheet" at the airport or border.

The move by the Saudi authorities was swiftly condemned on social network Twitter -- a rare bubble of freedom for millions in the kingdom -- with critics mocking the decision.

"Hello Taliban, herewith some tips from the Saudi e-government!" read one post.

"Why don't you cuff your women with tracking ankle bracelets too?" wrote Israa.

"Why don't we just install a microchip into our women to track them around?" joked another.

"If I need an SMS to let me know my wife is leaving Saudi Arabia, then I'm either married to the wrong woman or need a psychiatrist," tweeted Hisham.

"This is technology used to serve backwardness in order to keep women imprisoned," said Bishr, the columnist.

"It would have been better for the government to busy itself with finding a solution for women subjected to domestic violence" than track their movements into and out of the country.