EPIRBs and SARTs are both used to indicate your position in an emergency when you need rescuing at sea. The main difference between them is that they are used at different points of the rescue process because they are designed to communicate with different people.

EPIRBs communicate with satellites and are used at the start of a rescue when you first alert emergency services to your location. SARTs communicate with other vessels and are used when rescuers are on scene and homing in on your exact position.

What are the main differences between an EPIRB and a SART?

EPIRBs and SARTs are different pieces of safety equipment, designed for completely different purposes. I have summarised the differences in the table below, and you can read on for more details.

Received bySAR authoritiesOther vessels
Rescue stageInitialFinal
RangeUnlimited12 NM
Battery life48h96h (+12h)
Price$500+Around $500
Table showing the main differences between EPRIBs and SARTs

Who receives signals from EPIRBs and SARTs?

The most fundamental difference between EPIRBs and SARTs is in who they communicate with.

EPIRBs (Emergency Position Indicating Radio Beacons) communicate directly with international search and rescue coordinators. In the initial stages of a rescue, they send your GPS location to satellites which relay it onto authorities ashore.

SARTs (Search and Rescue Transponders) communicate with other vessels. They are used during the final stages of a rescue when a responding vessel is trying to locate the vessel in distress. It paints a distinctive pattern on a radar screen so that the responding vessel can home in on your exact location.

Do EPIRBs and SARTs have GPS integration?

EPIRBs are commonly equipped with GPS, giving them the ability to broadcast their location for satellites to receive. Older style EPIRBs did not use GPS, but orbiting satellites were able to triangulate its position instead.

Whichever type of EPIRB you have, the principle is the same. The signal from the EPIRB contains the position of the vessel in distress.

SARTs are different because they do not have GPS fitted. Instead, they are only useful when another vessel is close enough to detect the SART on its radar.

In recent years, AIS SARTs have started to become more common. This sort of SART does get a GPS position, which is transmitted within an AIS signal. They still communicate with responding vessels though, as the range of AIS is limited by the height of the SART. Instead of painting a pattern on a radar, AIS SARTs plant an AIS target on the screen instead.

What is the detection range of EPIRBs and SARTs?

EPIRBs are detected worldwide. They depend on a network of satellites in different orbits, together covering the entire surface of the globe. Assuming there is a clear line of sight up to the satellites, EPIRBs can be detected anywhere.

SARTs are different because they are designed to be detected by other vessels in the immediate vicinity. Radar SARTs can be detected by any vessel fitted with an X-band radar. AIS SARTs can be detected by any vessel fitted with an AIS receiver.

Most commercial vessels use their radar on a maximum range of 12 nautical miles. Some will have a second radar on a 24 nautical mile range when navigating in open areas. This means that a radar SART is only useful when another vessel is within either 12 or 24 miles, depending on the radar setting of the other vessel.

The range of AIS SARTs depends on the height of the antenna and atmospheric conditions. It is safe to assume that a properly mounted AIS SART can be detected within a similar range to a radar SART though.

What is the battery life of EPIRBs and SARTs?

EPIRBs and SARTs both have legal requirements for the length of time their battery should last.

The minimum battery life for an EPIRB is 48h. This is the minimum transmission time that you can expect. Once you activate the EPIRB, search and rescue services have 48h of transmission time to deploy assets to your location. After that, the EPIRB could continue operating, but there is no guarantee.

Hopefully search and rescue services will reach your position within 48h. Should it take longer, they can still work off of your last known position and deploy assets to the correct area.

SARTs are designed to last longer than EPIRBs. In their resting state, you will have 96h of standby time. This means that the SART is listening out for radar signals in the area. Once the SART detects a radar in the vicinity, it switched into transmission mode.

In transmission mode, a SART will last for a minimum of 12h. Transmission mode is used when vessels are close to your location. Vessels with operational radars should easily be able to reach your position within 12h once they are within radar range.

With SARTs, you can expect 96h standby time + 12h transmission time in total.

How does the price of EPIRBs and SARTs compare?

Both SARTs and EPIRBs are comparable in price. Standard prices for both are around $500.

Category 1 EPIRBs may cost more due to the additional cost of their float-free arrangements. For a fair comparison between EPRIBs and SARTs, however, it is better to compare a SART to a Category 2 EPIRB because both need to be activated manually.

At the time of writing, you can pick up an ACR GlobalFix V4 EPRIB from Amazon for $450. The similar SART, an ACR Pathfinder Pro is also available for $450 from Amazon.

Instead of buying an EPIRB, you could consider buying a PLB. PLBs are similar, but not identical to EPIRBs. You can read more about the differences between EPIRBs and PLBs in this article: What Is The Difference Between An EPRIB And A PLB?

If you did decide to buy a PLB instead, you can get similar functionality for a much lower price. Typical PLBs start at around $200, compared to nearer $500 that you would expect for an EPIRB.

What happens when you activate an EPIRB?

After activation, Category 1 and Category 2 EPIRBs perform the same. Category 1 has the potential to activate automatically, and Category 2 is manual activation only.

Either way, once you activate the EPRIB, it starts to transmit a signal on 406 MHz to the COSPAS SARSAT constellation of satellites.

This constellation consists of lots of satellites in different orbits. There are 5 in a low polar orbit, 10 in geostationary orbit, and over 40 others in medium altitude orbits. The goal is that the combined footprint from the satellites covers the entire surface of the earth.

Modern EPRIBs have built in GPS, so part of the signal they transmit includes their GPS position. Older ones do not have GPS, so when the satellites pick up the signal they triangulate it over a couple of orbits.

Regardless of the method of finding the position, the constellation of satellites now has the identification and position of the EPIRB that has been activated. It then sends that data down to control stations.

The control stations determine the nationality of the EPRIB from its identity, and then forward the distress signal on to the appropriate national Maritime Rescue Coordination Center (MRCC).

Once the identity and position is received by an MRCC, they compare the identification number of the EPIRB to their database. This gives them additional information about the vessel in distress which they can use to attempt contact with the vessel or its owners.

They then begin the process of searching for the vessel in distress and rescuing those on board.

Video about how EPIRBs work

What happens when you activate a SART?

SARTs should be activated when you are in your survival craft, with the intention of drawing the attention of other vessels.

Once you turn it on, it is in “listening mode”. In this mode, it is waiting to detect a pulse from an X-band (3cm wavelength) radar. As discussed previously, there will be enough battery power to operate in “listening mode” for at least 96h.

When the SART detects a pulse from an X-band radar, it immediately switches into transmission mode.

In transmission mode, the SART instantly returns a series of 12 pulses back to the radar. The time difference between the 12 pulses means that the SART appears as a series of 12 echoes on a radar screen.

Computer generated graphic of a radar screen showing an activated SART at range
In this image you can see what a SART looks like on a radar screen.

The searching vessel knows that the real location of the SART is on the echo closest to them, so they can plot a course to intercept.

As they get closer, the side lobes from the radar start to stretch the dots out to become wider. Eventually (less than 1 nautical miles from the SART), the 12 dots become almost full circles. The vessel then knows that the SART is close and they should be able to see any survival craft visually.

Video showing you how a SART works

What happens when you activate an AIS SART?

With AIS SARTs, it is a little different. Once it is activated, it searches for GPS satellites to determine its position.

It then broadcasts its own position and identity just like any other AIS device would.

Vessels in the area will then see the AIS SART as a target on their navigation systems. They can use the position to plot an intercept course and rescue with any survivors.

When is an EPIRB better than a SART?

EPIRBs are better than SARTs when there are no other vessels around.

Should you have an emergency, the EPIRB broadcasts your distress to the network of satellites, which can be reached from any location on earth.

This means that EPIRBs are especially useful when you are in a remote area like out at sea, or in an area that is infrequently navigated by other vessels.

From a different perspective, EPIRBs are also better than SARTs during the early stages of a rescue. Their signal should be sent to national Maritime Rescue Coordination Centers, who can activate sufficient resources for a successful rescue.

When is a SART better than an EPIRB?

SARTs are better than EPIRBs when there are other vessels around that are equipped with operational x-band radar.

The most common example is during the final stages of a rescue. Once other vessels arrive in the vicinity, a SART enables them to quickly find the people in distress.

Other vessels cannot directly detect the signal from an EPIRB, so the positional data would need to be relayed to responding vessels by the rescue coordinator. SARTs bypass that and give out signals that the other vessels can detect.

In addition to that, the battery life of an EPIRB means that it could have expired before rescuers arrive on scene. In the middle of the Pacific ocean, the 48h battery life may not be enough for it to be operational by the time help arrives.

Another example of when a SART could be better than an EPIRB is when you are navigating in a busy shipping area. The density of traffic means that the distress signal from the SART is likely to be picked up and acted upon quickly.

In this sort of situation, it is good if other vessels can see your distress themselves instead of waiting for a relayed signal from the coastguard.

Overall, SARTs are better than EPIRBs, in situations where there are other vessels around that are likely to detect the SART directly.

Should I carry an EPIRB or a SART on my boat?

Unless you are legally required to carry an EPRIB or a SART, the choice of which you carry is up to you.

EPIRBs and SARTs are both recognised as distress signals under the International Regulations for Preventing Collisions at Sea. The use of either one will mean that anyone detecting your signal should come and assist.

Carrying both is an ideal scenario, but clearly there are cost implications for doing so. At around $500 each, you are looking at over $1000 for both.

If I was to pick between them, I would choose to carry an EPIRB.

The reason I have chosen an EPIRB is that it should work in all situations, regardless of whether there are other vessels around or not. The direct satellite link, onwards to national maritime rescue centers just seems like the better option.

I understand that it means other vessels will not be able to respond as quickly as they could with a SART, but there are other options for that instead.

On my boat I like to always carry flares, and I always have a VHF onboard as well. Both of these can be used to alert vessels in the vicinity if I ever have an issue.

If the EPIRB needed to be activated, I would hope the position would be good enough to get other vessels close to me. After that, I would rely on my handheld VHF or flares to get their attention.