Some libraries are using a combination of technologies to extend (RFID based) self service into unmanned operation in order to extend library opening hours.
The concept of unmanned 'Open Libraries' has got significant traction on Denmark: “The open library concept demonstrates that it is possible to create institutions that are under the protection of the public and are designed to meet citizens’ needs in a flexible way.” The following article (from which the quote is taken) is a useful summary:
A New ‘Open Library’ Concept. By Jens Thorhauge, Director General, Danish Agency for Libraries and Media. Scandinavian Library Quarterly, Volume 44 NO. 4 2011
It stirred up some controversy among UK public libraries and there was a discussion thread on the LIS-PUB-LIBS discussion list. A good summary is in “Unstaffed Libraries (a contradiction in terms?)” Stop the privatisation of Public Libraries [blog] Thursday, 5 July 2012
It appears some UK public libraries are looking at the idea again in 2014