It's so frustrating. Your phone shows full bars of signal strength but it can't upload photos to Instagram or play Netflix or TikTok, let alone do anything business-related like sending emails or jumping into a video conference.
Phone black spots are a scourge of living in Australia's more remote areas because of the lack of infrastructure outside metropolitan areas.
But why does it happen in the inner suburbs and CBDs of our biggest cities?
Congestion and interference
In metro areas, there is a dense network of base stations, from the big cell antennas you see slapped on the sides and top of a tower or building, to microcells, which cover a much smaller area, such as a busy city intersection, or inside a shopping centre.
So, getting a signal usually isn't the problem, said associate professor Mark Gregory from RMIT University.
But "congestion in the network upstream" is a problem.
That goes for data, video calling and old-fashioned phone calls.
Dr Gregory said one of the worst black spots in Melbourne he'd experienced was the area just north of Melbourne Zoo, where the Upfield train line at Royal Park station and the number 58 West Coburg tram meet.
"Every day I watch people put their phones down for a minute, because they all know it's there," he said.
But black spots can occur anywhere because mobile phones are always searching for the next cell tower available to continue a call or video stream.
If it can't find one because something is blocking the signal, the call cuts out or the dreaded loading wheel appears on a video.
It's called interference, international telecommunications consultant Paul Budde said.
Big buildings, particularly those made of concrete, tunnels, dense foliage, and even tinted windows, can all block radio waves from reaching your phone, he said.
It's why it can be tricky to use your phone on a train; they're big metal boxes that can shield radio waves from getting in or out of the carriage.
A spokesperson from Telstra said trains are "made up of multiple layers of metal sheeting and even metallic window tints, and they often run through cuttings that put tonnes of soil and rock in between them and our mobile signal".
"This can mean short bouts of lost coverage in some places," they said.
Associate professor Ali Yavari from the School of Science, Computing and Engineering Technologies at Swinburne University said that windows on trains were modified to be more insulating to provide energy efficiency and UV protection, which weakens the signal trying to pass through the glass.
So, scrambling for a seat by the window might be fruitless.
Wi-Fi on trains could boost connectivity, Dr Yavari said, but "infrastructure cost, subscription and data bandwidth management, and certainly privacy and security concerns when using public Wi-Fi networks" were challenges.
But in a recent breakthrough in Europe, Siemens has developed a technology for the Austrian Federal Railways that not only permits the signal to pass through the glass, but will help a signal to pass through it, according to Mobile World Live.
Concrete walls, metal buildings, tunnels, and even vegetation can block a signal. Added to this, most base station antennas are designed to point down towards people and vehicles on the ground, not upwards at high rises.
But I have a strong signal
This can happen when there's congestion: crowds congregating at a concert, or sporting events, and even along busy streets.
Each phone is trying to use a slice of the radio waves, or spectrum. You can compare it to a highway; there might be enough lanes to handle the traffic most of the time, but the road can become congested during peak periods.
It's the same with the mobile networks. You can sit at a CBD train station at 10pm and have perfect reception but when the station is packed the link collapses.
Why can't the telcos just 'widen the road'?
Unfortunately, it's not that simple. The available spectrum used by phones is limited and is licensed by the federal government's Australian Communications and Media Authority. Phone companies can't just buy more.
ACMA sporadically auctions off the radio spectrum with prices reaching the billions of dollars, Mr Budde said.
Luckily, new technologies like 5G are more spectrum-efficient. So as more people move to 5G it will relieve the pressure on the older 4G network and soon-to-be-closed 3G network.
Is it getting worse?
No, black spots are reducing, Mr Budde said.
It might feel like they're increasing because when people use their phones more than ever, they're more aware of when they don't work.
Another reason it can seem like your phone drops out more than it used to is because of construction.
Dr Gregory said access points to the grid "needs to be continually checked and replaced, especially when someone puts up a big building or other obstruction next to it".
"The telcos are playing a catch-up game, trying to stay ahead of demand," he said.
A spokesperson from Optus said the company used "a combination of network performance data, modelling, customer feedback and crowd-sourced measures as inputs to prioritise mobile network builds".
However, you can't just build a new cell site overnight.
You need to find somewhere suitable, negotiate with the owner of the property, then advertise that you're building the site in case of objections.
The telcos also need to get planning permission from multiple authorities and arrange for power, cabling, and backbones to their internet. It can be an administrative nightmare taking years.
But not all is lost. Optus said it tries to increase the capacity of existing infrastructure "by making physical changes to the antennas or balancing the capacity between mobile towers".
And Telstra said customer complaints were investigated and responded to as necessary.
"In cases of expected congestion, such as the recent 2024 Australian Grand Prix, we deployed temporary mobile cells to provide additional capacity," a spokesperson said.
Mr Budde said black spots would continue to decrease as new technologies like Elon Musk's Starlink satellites become more widespread.
"There will be thousands of these satellites, over the next decade the whole earth will be covered."
Can I do anything to help myself out?
There's nothing you can do about a congested network, apart from complaining to your telco if there's a persistent problem.
But it's worth keeping in mind that your phone is actually a computer.
And like a computer, it needs to be rebooted from time to time.
So, instead of just leaving it on forever, try turning it off and on occasionally and keep the software up to date.
Apart from fixing security issues, the phone's maker may introduce new ways for the handset to better interact with the networks.
One fix that sometimes works is to turn airplane mode on and off, which will reset your connection with the network.
Turning off Wi-Fi when you're away from where you usually use it can also help.
A spokesperson from Vodafone said: "Some phones will try to automatically connect to open Wi-Fi networks that aren't actually providing data flow".
So, while the phone is stuck trying to get data from a non-existent source, it may just sit there and ignore the mobile network.
It could also be worth checking if a phone's SIM card is still sitting in the phone correctly by taking it out and popping it back in.
But it's more likely that just breaking the data connection and reconnecting does the trick.
Finally, a mobile phone's signal is only as good as the network it's connected to. So consumers could buy a cheap pre-paid SIM card from another provider and see if that works better, then consider making a permanent move.
But, phone companies are starting to do this too, Mr Budde said, by slowly allowing roaming.
"This means, for example, if you are an Optus user and don't have service in the area you're in, but Telstra does, you can roam to that other network.
"Australia is starting with this during emergencies. Next will be roaming in regional areas. This all helps to overcome what are black spots for one network but not for another."
Posted, updated
