How We Research
We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
If you want serious over-ear monitor headphones for critical listening, travel and long ANC sessions, choose Amazon Renewed Marshall Monitor III; if you need tiny in-ear sleep earbuds that stay comfortable for side sleepers and mask snoring all night, choose Anker Soundcore Sleep A20. These two are not really rivals — they solve completely different problems, and the "monitor headphones" angle only applies to one of them.
• Amazon Renewed Marshall Monitor III — biggest strength: full over-ear monitor-style listening with active noise cancelling, Dynamic Loudness tuning and a claimed 70 hours of wireless playtime with ANC on (100 hours without).
• Amazon Renewed Marshall Monitor III — biggest trade-off: it's a large, foldable over-ear headphone. It's not something you can roll onto your side with at 2 a.m.
• Anker Soundcore Sleep A20 — biggest strength: purpose-built sleep earbuds with 30 dB high-frequency noise reduction, twin-seal tips, Air Wing comfort for side sleepers and up to 80 hours from the case in Sleep mode.
• Anker Soundcore Sleep A20 — biggest trade-off: it has no active noise cancelling — it relies on passive blocking and masking — and it's a sleep-first product, not a monitoring tool.
• Who each pick is for: the Marshall is for listeners, travellers and anyone who wants one pair of headphones for music and noise cancelling; the Sleep A20 is for people who want audio in their ears while they sleep.
The Monitor III A.N.C. is, in plain terms, a listening headphone. Its job is to reproduce music well and to shut out the world while it does. The spec sheet leads with Marshall's "signature sound" and Dynamic Loudness, which adjusts treble, mids and bass at every volume level — that's the design thinking behind a monitoring-style headphone: keep the tonal balance usable whether you're listening quietly on a plane or loud at your desk. Soundstage spatial audio then pushes the music out of your head for a wider, more immersive presentation. If you care about how a mix sits, about separation, about hearing detail rather than just a beat, this is the half of the comparison that actually speaks that language.
The noise cancelling side is just as deliberate. Marshall upgraded the ANC over the previous generation, and the headphone continuously measures ambient noise to adapt what it blocks. There's a transparency mode too, so you can let the outside back in without taking the headphones off. Battery is the headline number: 70 hours of wireless playtime with ANC running, and 100 hours with it off. That's a figure that changes how you use a product — you stop thinking about charging. It charges over USB-C, and the box includes a USB-C to 3.5mm audio cord, so you can go wired when you want to.
Build-wise, it's rugged, foldable and comes with a premium hard case. The 8.8-ounce weight and soft ear cushions are meant for all-day wear, and the over-ear design physically surrounds your ears rather than sitting inside them. Media controls are on the headphone itself.
Who should buy it: commuters, travellers, home listeners and anyone who wants a single pair of over-ear headphones for music, calls and noise cancelling, with a wired fallback. Who should skip it: side sleepers, people who want earbuds they can leave in overnight, and anyone who needs their audio to be invisible. This is a visible, over-ear product. As a renewed item it also carries a 90-day limited warranty, which is worth knowing before you commit.
The Sleep A20 is the opposite end of the spectrum, and it's honest about it. The first thing to understand is that it does not have active noise cancelling — the spec sheet says so outright. Instead it uses a four-point noise masking system with twin-seal ear tips that Anker says block three times more passively, aiming at snoring, pets and general ambient noise. That's a masking philosophy rather than an ANC philosophy, and it makes sense for a product whose job is to keep you asleep rather than to make a commute quieter.
Comfort is where the design earns its keep. Ultra-soft materials, the Air Wing and a 3D ergonomic shape are all there to make side sleeping pressureless — the classic failure mode of normal earbuds. The kit includes three pairs of breathable ear tips, four pairs of sealed ear tips and three ear wings, so you're tuning fit rather than accepting it. Color is Slumber Beige, and the whole thing is in-ear with rounded tips and wings.
The feature set is sleep-specific. The soundcore app plays binaural beats to help you drift off, with continuous loop-free audio so nothing jars you awake. MEMS sensors track your sleep and produce reports in the app. Battery is split by mode: up to 14 hours per charge and 80 hours from the case in Sleep mode, or 10 hours of Bluetooth playtime extendable to 55 hours with the case. Bluetooth 5.3, a 15-meter range, touch controls and a small 6.6 x 6.6 cm case round it out. Charge time is 4.5 hours, and the case holds a 580 mAh battery. Warranty is 18 months.
Who should buy it: side sleepers, light sleepers, people sharing a bed with a snorer, and anyone who wants sleep tracking without wearing a watch. Who should skip it: anyone expecting active noise cancelling, and anyone who wants one headphone for music-first listening. This is not a monitor headphone. It's a sleep tool.
Side-by-Side: Which Should You Choose?
• Best for critical listening and monitor-style sound → Amazon Renewed Marshall Monitor III. Dynamic Loudness, Marshall signature tuning and Soundstage spatial audio are built for how music sounds.
• Best for noise cancelling → Amazon Renewed Marshall Monitor III. It has true Active Noise Cancellation that measures ambient noise continuously, plus transparency mode. The Sleep A20 has none.
• Best for sleep and side sleeping → Anker Soundcore Sleep A20. Air Wing, ultra-soft materials and a 3D ergonomic in-ear shape are designed around lying on your side.
• Best for battery life → Amazon Renewed Marshall Monitor III on raw hours (70 with ANC, 100 without), though the Sleep A20 wins on sleep-mode endurance with 80 hours from the case.
• Best for a wired option → Amazon Renewed Marshall Monitor III. It ships with a USB-C to 3.5mm audio cord.
• Best for sleep tracking → Anker Soundcore Sleep A20. MEMS sensors and app-based sleep reports.
• Best for travel and packing → Amazon Renewed Marshall Monitor III. Foldable design and a protective hard case, with a rugged build for everyday wear.
• Best if you want audio you can wear all night without noticing it → Anker Soundcore Sleep A20.
• Best if you want one product to do everything → honestly, neither. These are specialists. Pick the problem you actually have.
In my opinion, if the words "monitor headphones" are the reason you're here, buy the Amazon Renewed Marshall Monitor III. It's the only one of the two that is actually a headphone in the listening sense — ANC, spatial audio, tonal tuning at every volume, wired fallback and battery life measured in days rather than hours. I'd recommend the Anker Soundcore Sleep A20 only if your real problem is sleep: a snoring partner, a noisy street, or the inability to lie on your side with earbuds in. Buy for the job, not for the category. And check the current price on Amazon before deciding, since renewed stock and pricing move around.
how to check headphones battery on iphone
On an iPhone, paired Bluetooth headphones usually show a battery indicator in the Bluetooth settings list or on the battery widget on your home screen. Some brands, like Marshall, also expose battery status through their own companion app. The Monitor III A.N.C. is rated for 70 hours with ANC and 100 hours without, so you'll be checking it far less often than typical earbuds.
how to check headphones battery
The general method is the same across platforms: look at your phone's Bluetooth menu, a battery widget, or the manufacturer's app. The Sleep A20 splits its figures by mode — up to 14 hours per charge and 80 hours from the case in Sleep mode, or 10 hours of Bluetooth playtime extendable to 55 hours with the case — so its app is the clearest place to read the real number.
how to check headphones
Checking a headphone before you buy comes down to three things: fit type, noise control and battery. The Marshall Monitor III is over-ear with active noise cancelling and a foldable, rugged build. The Sleep A20 is in-ear with passive noise cancellation, a 3D ergonomic shape and Air Wing comfort aimed at side sleepers. Match the fit to how you'll actually wear it.
how to check headphones mic
To check a mic, pair the headphones, make a call or voice recording and listen back. The Marshall Monitor III includes a microphone and media controls on the headphone, and it ships with a USB-C to 3.5mm audio cord if you'd rather go wired. The Sleep A20 is built around sleep audio and Bluetooth 5.3 streaming rather than calls, so don't buy it as a headset.
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