Both install on your main water line, watch the water coming into the house and close a built-in valve when they see a leak. The deciding question is your pipe size.
Our picks at a glance
From published specs and our sizing rules. Not lab tested.
- 1
Best for 3/4 in mains
Moen Flo Smart Water Monitor and Automatic Shutoff (3/4 in)
Check price at MoenPaid link
- 2
Best for 1 in mains
Moen Flo Smart Water Monitor and Automatic Shutoff (1 in)
Check price at MoenPaid link
- 3
Best for 1-1/4 in mains
Phyn Plus Smart Water Assistant and Shutoff (2nd gen)
Check price on AmazonPaid link
If yours is 3/4 in or 1 in, buy the Moen Flo: around $624 for 3/4 in and $676 for 1 in at Moen's store, and it is the device behind the LexisNexis study that found 96% fewer water claims. For a 1-1/4 in main, the Phyn Plus (2nd gen) fits where the Flo does not.
Either one needs a plumber to cut it into the main. Budget for that on top of the device.
Top picks, and why
Moen Flo Smart Water Monitor and Automatic Shutoff (3/4 in)
Monitors flow, pressure and temperature, shuts off automatically, no hub. Around $624 at Moen. Two 3/4 in tailpieces included.
- Closes its own valve when it detects a leak
- Watches flow, pressure and temperature
- No hub needed
- Plumber install recommended
- Sized for a 3/4 in main line
About $624 at Moen, checked Oct 12, 2026
Check price at MoenPaid link. We earn a commission at no cost to you.
Moen Flo Smart Water Monitor and Automatic Shutoff (1 in)
The same Flo for a 1 in main line, around $676 at Moen.
About $676 at Moen, checked Oct 12, 2026
Check price at MoenPaid link. We earn a commission at no cost to you.
Phyn Plus Smart Water Assistant and Shutoff (2nd gen)
Pressure-sensing detector with a built-in shutoff for mains up to 1-1/4 in, no app subscription required, $500 to $1,000. Adapters sold separately.
- Built-in shutoff valve closes on a leak
- Fits main lines up to 1-1/4 in
- No app subscription
- Professional install
$500 to $1,000, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
Compare every pick
Paid links: we earn a commission if you buy, at no cost to you. Amazon prices change often, so we show a range and link to the live price.
Side by side
Moen Flo: models for 3/4 in (900-001) and 1 in (900-006) mains, monitors flow, pressure and temperature, closes its own valve, rated to 175 psi, no hub. Around $624 and $676 at Moen.
Phyn Plus (2nd gen): for mains 1-1/4 in or smaller with a 1 in connection and adapters (1/2, 3/4, 1 and 1-1/4 in) sold separately, pressure-sensing leak detection, built-in shutoff valve, no subscription needed for the app, professional install. Price: $500 to $1,000.
Both connect to a phone app for leak alerts. Both are a plumbing job, not a plug-in.
How to pick
Measure your main first. Look where the line enters the house, usually near the water heater or in the basement.
3/4 in or 1 in: Moen Flo. It has the insurance study behind it, and some insurers run programs for it: Stand Insurance offers discounts for an active Flo and Liberty Mutual has a Moen install program. Ask yours.
1-1/4 in: Phyn Plus, which covers that size with an adapter.
Moen Flo Smart Water Monitor and Automatic Shutoff (3/4 in)
Around $624 at Moen. The device in the LexisNexis claims study.
- Closes its own valve when it detects a leak
- Watches flow, pressure and temperature
- No hub needed
- Plumber install recommended
- Sized for a 3/4 in main line
About $624 at Moen, checked Oct 12, 2026
Check price at MoenPaid link. We earn a commission at no cost to you.
Phyn Plus Smart Water Assistant and Shutoff (2nd gen)
$500 to $1,000, adapters extra.
- Built-in shutoff valve closes on a leak
- Fits main lines up to 1-1/4 in
- No app subscription
- Professional install
$500 to $1,000, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
Add sensors where leaks start
A main-line shutoff catches big leaks anywhere. Cheap battery sensors add a loud local alarm right at the water heater, washing machine and under sinks, where slow leaks often start.
GoveeLife Smart Water Leak Detector 1s, 3-Pack with Gateway
Three sensors, 105 dB alarms and a Wi-Fi gateway for under $100.
- Three sensors with 105 dB local alarms
- Wi-Fi gateway sends app, SMS and email alerts
- IP67 sensors rated for up to 5 years per battery
- Alerts only, no automatic shutoff
- Gateway needs 2.4 GHz Wi-Fi
Under $100, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
The bottom line
From published specs and our sizing rules. Not lab tested.
- 1
Best for 3/4 in mains
Moen Flo Smart Water Monitor and Automatic Shutoff (3/4 in)
Check price at MoenPaid link
- 2
Best for 1 in mains
Moen Flo Smart Water Monitor and Automatic Shutoff (1 in)
Check price at MoenPaid link
- 3
Best for 1-1/4 in mains
Phyn Plus Smart Water Assistant and Shutoff (2nd gen)
Check price on AmazonPaid link
Frequently asked questions
Is Moen Flo or Phyn better?
For a 3/4 in or 1 in main, Moen Flo: direct fit, no hub, and the LexisNexis study found 96% fewer water claims in Flo homes. For a 1-1/4 in main, Phyn Plus, which supports that size with an adapter.
How much does a Moen Flo cost?
Around $624 for the 3/4 in model (900-001) and $676 for the 1 in model (900-006) at Moen's store, plus plumber installation.
Does Phyn require a subscription?
No subscription is required for the Phyn app.
Can I install a Moen Flo or Phyn myself?
Both are cut into the main water line, so a licensed plumber is recommended.
How do I tell if my main water line is 3/4 in or 1 in?
Wrap a string around the pipe near the main shutoff and measure it. On copper or copper-tube-size PEX, about 2.75 in around means 3/4 in, about 3.5 in means 1 in, and about 4.3 in means 1-1/4 in. PEX usually has its size printed on the pipe.
How does Moen Flo detect a leak compared with Phyn Plus?
Moen Flo measures flow, pressure and temperature on the main line and closes its own valve when it detects a leak. Phyn Plus (2nd gen) uses pressure sensing to detect leaks and closes its built-in shutoff valve. Both send leak alerts to a phone app.
What water pressure can a Moen Flo handle?
Moen rates the Flo to 175 psi. Most homes run far below that, since the IPC and UPC plumbing codes call for a pressure-reducing valve when supply pressure is over 80 psi. Because the Flo monitors pressure, its app also shows if your house pressure is running high.
Where does a Moen Flo or Phyn Plus get installed?
On the main water line just after the main shutoff valve, before the line branches to the water heater and fixtures, so all the water entering the house passes through it. That is usually where the line comes in, in the basement, garage or utility room. It is a plumbing job, so a licensed plumber is recommended.
Do I still need water leak sensors with a Moen Flo or Phyn?
They add a second layer. A main-line shutoff catches leaks anywhere in the house, while battery sensors sound a local alarm right where slow leaks start: the water heater, washing machine and under sinks. The Govee 3-pack includes three sensors with 105 dB alarms and a Wi-Fi gateway for phone alerts.
Does a Moen Flo lower homeowners insurance?
It can. Stand Insurance offers discounts for an active Flo and Liberty Mutual runs a Moen install program, but insurers do not publish a set percentage, so ask yours. The LexisNexis study behind those programs found 96% fewer water claims in Flo homes the year after installation.
6 products are linked on this page. We have not lab-tested these products; picks are based on published specifications and our sizing rules. Amazon prices change, so we show a range and link to the live price. See our disclosure.
Size it for your home
Marcus Reed
Founder and Editor, CrunchYourDollars
Marcus Reed builds the sizing tools on CrunchYourDollars. He is a software engineer with a long-running PC hardware and power supply habit, which is where the watts, watt-hours and surge math on this site comes from. Product specs are pulled from manufacturer data sheets, electricity rates from the U.S. Energy Information Administration, and water chemistry rules from the Water Quality Association. He is not a licensed electrician or plumber: the tools show the math and the matching models so you can make the call, and anything involving your electrical panel should be checked by a licensed pro.
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