In the summer of 2008, a three-year-old girl accidentally fell into her family's swimming pool while playing in the yard. Her parents were close by, but unaware of what had happened; there had not been a loud splash or any other sign that there daughter was in trouble.

As soon as the girl entered the water, however, she activated a sonar-based alarm system which promptly issued an alert. The parents rescued their daughter, and the grateful father let the company know about the incident; the company said the alarm had already saved eight other children in similar circumstances.

Although swimming pools are required to meet several standards to improve safety, unexpected tragedies can still occur. According to the Centers for Disease Control, about one in five drowning deaths in the United States is a child under the age of 14. Drowning is a leading cause of death for children between the ages of one and four, and most of these drownings occur in swimming pools.

Pool alarms add another protective option to more passive measures such as fencing and self-latching gates. Connecticut has required newly installed or updated pools to have alarms since 1999.

These systems sound an audible warning if someone gets past a pool barrier or if a large object enters the water. Some alarms are connected to a wearable device. Homeowners can also choose to have multiple different alarm types installed at their pool.

Entry alarms

Some alarms are installed on gates that access a swimming pool. If a door or window at the home opens onto a pool area, it can also be alarmed. Nick Gromicko, writing for the International Association of Certified Home Inspectors, says some pet doors can also have alarms installed.

This type of alarm typically uses infrared beams or a magnetic connection. When the beam or connection is broken, it sets off a loud alarm to let you know that someone has entered the area near the pool. Caroline Maurer, writing for the home safety resource Safewise, says entry alarms also tend to be less expensive than other types of pool alarms.

Entry alarms, and other types of pool alarms, may come with a wireless remote. Saltwater Pool & Spa, a resource for saltwater swimming pool and hot tub owners, says this feature will not only alert you directly but also allow you to set or deactivate an alarm.

Pool alarms mounted at entry points to the home will typically double as home security devices. The pool care resource Swim University says the alarm can usually be linked to a smartphone or a smart home device to let you know if there is a problem, even if you are out of earshot of the audible alarm.

Alarms usually have a "pass-through" button that allows you to briefly deactivate the alarm when an adult uses the door or gate. Some alarm systems will only activate if a gate or door is left open for several seconds.

The most significant drawback of this type of alarm is that it might not register every entry into the pool area. For example, Maurer says children may be able to climb over a fence to bypass the gate.

Alarms in the water

Some pool alarms are installed directly in the water to detect whether a child or pet has fallen into the pool. These alarms are usually configured to sound when an object weighing approximately 15 pounds enters the water.

The alarms can be mounted on the side of the pool with a sensor extending into the water. Swim University says the device measures disturbances in the water and sounds an alarm if it detects waves that are likely associated with a child or pet falling into the pool.

Naturally, you won't want the alarm blaring during a pool party with a lot of water movement. For this reason, you'll have the option of removing the sensor arm or putting the device in sleep mode.

Each unit will be limited to a certain range. Saltwater Pool & Spa says you may need to invest in multiple devices in order to effectively cover the entire pool.

Floating alarms are small devices that will drift on the surface of the water and detect water movement. Gromicko says floating alarms involve an electrical circuit which is closed when a contact is immersed by a wave, presumably after something splashes into the water. Once the circuit is completed, it triggers an alarm.

While the sensitivity of the alarm can be adjusted, it can be tricky to arrive at the right setting. Maurer says systems based on water movements might issue false alarms when the wind stirs up the water.

Some alarms are sonar-based, located underwater to detect when a person enters the water. Gromicko says other types of underwater alarms will detect pressure changes caused by waves.

Wearable alarms

Designed to easily strap on to a child's wrist, these alarms can be locked so the wearer cannot easily remove them. Maurer says they can offer a parent peace of mind if they are working in the yard while a child plays nearby.

The parent carries the alarm, which will go off if the sensor on the wristband gets wet. Swim University says some models also have a proximity alarm and will go off if the child wanders too far away.

The main drawback of a wearable alarm is the potential for false alarms. Gromicko says the sensor may activate if it becomes wet for another reason, such as a child washing his or her hands. Maurer says a parent will also have to remove the wristband to take a child for a supervised swim, and that a wearable alarm will offer no protection if a child manages to get it off or a parent forgets to put it back on.

Precautions

While pool alarms can offer some safeguards and potentially be a lifesaver, homeowners should not rely on them as a sole way of keeping children safe. The Consumer Product Safety Commission has said that alarms should not be a substitute for proper supervision or physical barriers such as pool covers.

Alarms are also vulnerable to certain human errors. For example, a homeowner might shut off an alarm to go for a swim and forget to turn it back on.

The American Red Cross says pool alarms should be considered a secondary safety measure, and should be installed high enough to be out of reach of children. The organization recommends combining pool alarms with safety precautions such as barrier fencing, flotation devices, teaching children how to swim, and ensuring that family members know what to do in case of a water emergency.