The International Pilot Project for Technology Co-operation in landmine detection is a multinational effort with participation from government agencies and research institutes from Canada, the USA, the UK, the Netherlands and the European Commission. One goal of the pilot project is to provide technical information on a number of commercial metal/landmine detectors to sponsors and end users of such technology, to help them make informed decisions about equipment selection in humanitarian demining. To this end, a series of laboratory and field tests have been conducted by the project team at various locations. A significant component of these tests was the tests conducted in a controlled laboratory environment at the Defence Research Establishment Suffield, Alberta, Canada. These tests focused on a detector's ability to detect objects in air (also referred to as its in-air sensitivity) and assessed how much this sensitivity would be affected by various parameters that model some real-world conditions, such as the presence of moisture, variation of sweep speed, electronic drift and so on. While a detector's ability to detect objects in air does not always indicate its ability to detect objects buried in the ground, such controlled tests are very useful in comparing certain basic performance factors of the electronics of a given detector and in understanding a detector's performance in the field. Six different in-air tests were conducted on 29 models of commercial-off-the-shelf metal detectors from a number of manufacturers. The paper discusses the methodology and results of these tests.