Conclusion: No / inconclusive evidence found to make an evidence statement; effect unknown
An evaluation of swimming pool alarms by CPSC (Whitfield, 2000) finds that subsurface pool alarms were more consistent in alarming and less likely to false alarms than surface pool alarms; when a test object, intended to simulate the weight of a small child, was pushed into the pool, the subsurface sensors detection were most reliable.
A systematic review of Chalmers et al. (2004), which also takes into account the review of the Harborview Injury Prevention & Research Center
(http://depts.washington.edu/hiprc/practices/topic/drowning/pool alarms.html) identified no empirical evidence of the effectiveness of pool alarms in preventing the drowning (or near drowning) of children in domestic pools. It points out that one problem with alarms is their susceptibility to being activated by events other than the submersion of children, such as wind and rain, leading, presumably, to reduced vigilance due to high levels of false alarms.
Also a more recent review of Weiss et al. (2010) found no formal studies demonstrating the effectiveness of pool alarms to prevent drowning in children. The same conclusion is drawn in the WHO Guidelines for safer recreational water environments (2006).
Recommendations (for research & practice)
For Practice and Policy
CPSC (Whitfield, 2000): A pool alarm can be a good additional safeguard in that it provides an additional layer of protection against child drownings in swimming pools. Since pool alarms rely on someone remembering to activate them each and every time the pool is in use, they should not be relied upon as a substitute for supervision or for a barrier completely surrounding the pool. A remote alarm feature that will sound inside the house is important to have with a pool alarm.
AAP (2010): Although data are lacking, families can be advised to consider supplemental pool alarms as additional layers of protection; however, pool alarms are no substitute for adequate fencing.
For further Research
Evidence review examining structural housing deficiencies, involving factors related to construction, design, installation, and lack of monitoring or maintenance, found that pool alarms were interventions in need of formative research, both in efficacy and design (Jacobs et al, 2009; Di Guiseppi et al., 2010).
Review Date: 01/03/2011
Articles (reviews) and reports were included that were published between 1992 and 2011, in English and Dutch. The outcomes of the study were reviewed by the Dutch Consumer Safety Institute.
Strategy: An online literature search was performed by a researcher of the Consumer Safety Institute and after this a more thorough search was performed by the documentation centre of CSI (Catalog CenV, Pubmed, Injury lit, Google, Websites, 'Grey' literature). Results of each search were compared on differences and potential missed studies were added. First the titles and then abstracts were scanned in order to include relevant studies. In the case of insufficient information obtained from abstracts the full text articles were obtained. Irrelevant studies were excluded, i.e. the article does not comprise  the evaluation or effectiveness,  the prevention of child injuries,  the specific preventive measure studied. Relevant articles were scrutinized and background documents were created. In addition, relevant references of included articles were checked on new and relevant articles (i.e., snowball search).
The outcomes of the study were reviewed by an expert in the field of child safety in the summer of 2011.
An evaluation of swimming pools alarms (version 1.0)
Troy W. Whitfield (2000)
Technical report : prevention of drowning (version 1.0)
Jeffrey Weiss (2010)
Drowning, near-drowning and other water-related injury : literature review and analysis of national injury data : report to accident compensation corporation (version 1.0)
David Chalmers, Brownwen McNoe, Shaun Stephenson, ... [et al.] (2004)
Guidelines for safe recreational water environments : volume 1. coastal and fresh-waters (version 1.0)
Housing interventions and health : a review of the evidence (version 1.0)
David E. Jacobs, Andrea Baeder (2009)
Policy statement - prevention of drowning (version 1.1)
Committee on injury, violence, and poison prevention (2010)
Housing interventions and control of injury-related structural deficiencies : a review of the evidence (version 1.0)
Carolyn DiGuiseppi, David E. Jacobs, Kieran J. Phelan ...[et al.] (2010)