Last spring, a sandwich shop two streets away from the author’s home was without internet for almost an entire Saturday. The owner wasn’t bothered by the outage itself, but rather by the menu display above the till, which had turned light grey and remained that way whilst a queue of customers stared at it. He restarted the router, restarted the TV and, figuratively speaking, restarted himself, to no avail.
That afternoon cost him perhaps forty orders, lost due to confusion and customers walking away. The solution turned out to be a two-minute setting, hidden within the software, which sums up the whole category: the screens are reliable, whilst the software behind them is not always so.
A useful check before making any payment is to ask the supplier just one question: to demonstrate what happens to the product when the network is disconnected. Most will switch to a slide about templates. Those selling the best digital signage software (best digital signage software) will answer the question directly, because local storage makes the difference between a screen that sells and a rectangle hanging pointlessly on the wall.
What, specifically, goes wrong when the connection drops?
Three things go wrong, in a specific order, which every buyer should be aware of.
Firstly, scheduled content stops playing, and the lunch menu freezes on the slide that was playing at that moment. Secondly, dynamic feeds become out of date or disappear altogether, which is why many weather widgets and social media feeds turn into empty black boxes as soon as they can no longer contact the server. Thirdly, and this is the most unpleasant scenario, any screen that needs to query a cloud server simply to play a local video file will stop playing it.
The engineering solution is local storage that keeps the entire playlist on the device. The player continues to play from memory, and the cloud only comes into play when a change is sent. The cloud is a delivery method, not the system’s engine, and anyone who reverses these two roles is, in practice, selling a remote control with extra steps.
The significance of the issue beyond a single shop is evident in the seriousness with which public institutions treat network resilience. The National Institute of Standards and Technology (National Institute of Standards and Technology) publishes cybersecurity frameworks in the United States, including Cybersecurity Framework 2.0, which incorporate functions dedicated to incident response and recovery and are based on the premise that incidents do occur and that systems must be able to continue functioning. The menu bar is a lower-stakes version of the same problem.
What distributed systems theory says about a screen without a network
The choice a player makes when they lose connection to the server was formulated theoretically a quarter of a century ago. In 2000, at the ACM symposium on the principles of distributed computing, Eric Brewer presented a conjecture that became known as the CAP theorem: a distributed system cannot simultaneously guarantee consistency, availability and tolerance to network partitioning. Seth Gilbert and Nancy Lynch formally proved the result in 2002, in an article published in ACM SIGACT News. In practical terms, when the link between two parts of a system is severed, each part must choose between responding with the data it has – which may be out of date – and refusing to respond until it can verify that the data is up to date.
A menu panel that turns grey made the second choice, although for it this is the wrong one. The software treated the content as information that must be confirmed by the server before display and preferred to show nothing rather than display something that might be out of date. For a menu, the cost of information that is a few hours out of date is virtually zero, whilst the cost of a blank screen is a queue of puzzled customers. The three tests proposed in the following section essentially check which choice the software designer made between availability and consistency, and how well the two aspects are reconciled once the network is back online.
Brewer revisited his own theorem in 2012, in the journal IEEE Computer, in an article that clarifies its limitations. The ‘two out of three’ formula oversimplifies matters, he pointed out, because partitions are rare, and the choice between consistency and availability can be made separately for each operation, rather than as a single decision for the entire system. His example is the cash machine, which often continues to dispense cash when it loses connection with the bank, up to a certain limit, and reconciles the balances later. Availability is prioritised where the risk can be limited, whilst consistency is maintained where an error would be too costly.
Applied to screens, this nuance shows that the rule ‘display whatever is in memory’ is, in turn, too simplistic. A menu featuring standard products can run from memory for days on end. A promotion with an expiry date, a price that has changed or information about allergens are examples of content where an outdated version could lead to a complaint or a legal issue. Well-designed software allows the administrator to specify, for each item, how long it can be displayed without confirmation from the server and what appears in its place after this period. The right question to ask the supplier thus becomes more precise than simply testing whether the cable has been disconnected: what content can expire whilst offline, and who decides this?
The framework has limitations that need to be stated. The CAP theorem describes distributed systems with replicated data and says little about the most common causes of a black screen in a shop, such as a faulty power supply, a failed update or a cable accidentally being unplugged. It also assumes a clear partition, whereas real-world networks often degrade gradually, with a slow and unstable connection that is harder to deal with than one that has completely failed. The theorem helps in formulating questions for the supplier, without replacing testing on the actual device.
The three-question test before signing
The test doesn’t require a laboratory; it just requires a sales representative to be put in a slightly awkward situation.
- The disconnection test: the provider is asked to unplug the network cable during the demonstration and carry on talking. Does the screen retain the last playlist or go blank?
- The recovery test: when the network comes back, does synchronisation resume automatically, or does someone have to go to the device and intervene?
- Handover test: can a manager who has never seen the admin panel publish a promotion from their phone in under five minutes?
Their importance follows this order. The disconnection test is non-negotiable, and the handover test shows whether the system will actually be used after six months, when the novelty has worn off and all that’s left is yet another password to remember.
A fourth test is worth adding, as the shop’s connection is just one of the links that can fail. In October 2025, a fault in the DynamoDB service’s automated DNS system affected the us-east-1 region of Amazon Web Services for approximately 14 and a half hours, according to the report published by the company following the incident, and numerous online services that relied on that region became unavailable, even though their customers’ networks were functioning normally. The annual outage report published by the Uptime Institute in May 2026 notes that, over nine years of tracking publicly reported incidents, approximately two-thirds originated from third-party IT service providers and data centres, such as cloud, internet and telecommunications companies. The same report shows that 57 per cent of respondents to the 2025 survey estimated the cost of the most recent major outage at over $100,000.
For a shop, the consequence is that the screen must remain functional even when the local Wi-Fi is working but the provider’s server is unresponsive. The two situations are not technically identical, as a player can correctly handle a complete lack of network connectivity but may freeze when the network is present yet the server returns errors. You can ask the provider where they host their platform, what the player does when the central server is unavailable, and whether they publish an incident log; a precise answer to these questions is a better indicator than any general guarantee of availability.
Choosing the hardware comes after choosing the software
Many buyers spend a great deal of time agonising over the choice of media player and then select the software at the last minute. The order should be reversed, as the software determines which players can be used, and this constraint persists long after the hardware appears to be obsolete.
In practice, the breakdown looks like this. Players built specifically for this purpose are the safest choice for critical displays, as they are designed to do one thing and not be tampered with. Consumer streaming sticks are cheap and suitable for a single display, but they are designed for entertainment and are updated according to someone else’s schedule, which can sometimes lead to a surprise on a Tuesday morning. User-supplied Android devices fall somewhere in the middle, and this is where most small operators end up.
One detail is worth noting: if screens display regulated data, such as employee information on a screen in the staff room, the player’s security level matters. The General Services Administration (General Services Administration) maintains procurement guidelines in the United States regarding IT security requirements for government buyers, which can serve as a reasonable benchmark for expectations of a supplier, even outside the public sector.
A common mistake during the initial installation
The author’s first setup consisted of a spare monitor, a cheap USB stick and a cloud-only tool, which looked great in the browser. The system worked for about a week, until the router had a bad afternoon and the screen displayed a loading animation for three hours.
The lesson to be learnt from rebuilding the system was that the fault did not lie with the router. The software had been evaluated based on the admin panel – that is, the part the buyer rarely sees – rather than the player, which is the part customers look at all day long. No one in the shop sees the content library; everyone sees the screen, so it is the screen that must be judged.
The second lesson concerns time. A playlist that is set up and then forgotten looks outdated within a month, because a menu that never changes looks like a menu that nobody is looking after. Thirty minutes set aside each week in the calendar, at the same time, and treated as part of the routine, do more for the effectiveness of a screen than any comparison of features.
Where the industry is heading and why it matters
Edge computing is the technical term for what has been described above, and the technology is moving from server rooms to screens. The IEEE (IEEE), the professional organisation behind a large proportion of the standards for networked devices, has for years been documenting the shift towards local processing, rather than relying on a remote data centre. For a shop owner, this means that devices are becoming increasingly resilient to poor connections, and this resilience should be expected as a baseline feature, rather than something you have to pay for as a premium service.
Negotiations are changing accordingly. A supplier that still makes offline playback conditional on an enterprise subscription is saying something about the architecture of its product, and that message is worth listening to.
How to assess a supplier, beyond the demonstration
The tests above assess the product, but a software contract also binds the shop to the company that produces it. A supplier that disappears after two years leaves behind players that no longer receive updates and content locked in a format that nobody can read anymore. A few simple checks reduce this risk: how long the company has been in business, how often it releases updates, whether it undergoes independent security audits, and what happens to playlists and uploaded files when the subscription ends. You should try exporting the content into a standard format before signing up, as an export function that exists only on paper is of no use to anyone on the day of migration. Where the provider offers a trial period, it is worth using it on the actual equipment in the shop, with the actual network and with a regular member of staff using the admin panel, as a demonstration carried out on the sales representative’s laptop shows the product under the most favourable conditions, whereas the shop will use it under the most ordinary conditions, with an old router and a connection shared with the payment terminal.
To draw up an initial list of providers, the software category in the Jasmine Directory outlines the criteria against which manufacturers should be compared, ranging from delivery and pricing models to the company’s length of operation, active product support and the fate of data following the termination of payment. The limitations of such a listing must be made clear. It confirms that the company exists, that it operates in the stated field and that it can be contacted, but it does not test the offline behaviour of any product, does not guarantee the quality of support and does not constitute a recommendation. The ‘unplugged test’ remains the buyer’s responsibility and cannot be delegated to any external source.
The same problem, outside the shop
The question with which this article concludes – about technology that silently fails in front of the customer – has an answer that few business owners take into account: public information about their own company. A shop’s opening hours, telephone number and address exist in dozens of copies – on online maps, in directories, on social media and in delivery apps – and each copy is, in the terms of the CAP theorem, a permanently available replica, which can, however, become out of date. When the shop changes its Saturday opening hours, some copies are updated, whilst others retain the old times. The customer who arrives to find the door closed has encountered the same type of fault as the one standing in front of the grey screen, with the difference that the owner never sees this screen.
The solution is similar to that described for playlists. The analysis in what makes an entry in a business directory credible suggests maintaining a canonical record of company data, against which all other copies are verified, and a quarterly audit of the main listings, more frequently for companies whose data changes frequently. The weekly thirty-minute slot set aside for screen time could also include this check once a month. No audit can guarantee that all copies are correct at all times, as some platforms update their data according to their own schedule; however, a canonical record ensures that errors can be identified and corrected, rather than being discovered by a customer.
What is actually worth buying
For a shop set up from scratch, the sensible choice is software with native offline storage, supporting at least two types of device so that the shop does not rely on a single player, and featuring a mobile management app that can be used from the warehouse. The equipment should be kept simple: a good player for each screen, connected by cable where possible and labelled with a piece of adhesive tape, so that the next person knows what each cable does.
Here’s the test the sandwich shop should have carried out: switching off the Wi-Fi one Tuesday morning and observing what the customers see. If the screen holds up, it was a good purchase; if it doesn’t, the lesson is worth more than the money recouped.
When was the last time a piece of technology in your own business failed, silently, in front of a customer, without anyone giving a warning before it was too late?
Thus, the problem of the screen turning grey turns out, on closer inspection, to be a specific instance of the choice between displaying potentially outdated information and displaying nothing at all – a choice that any distributed system makes when it loses connection with its source. It can be concluded that good display software is recognised by the way it handles this choice, with content running from memory, expiry dates for sensitive information and automatic reconciliation when the network is restored, and the same rigour, applied to public copies of the company’s data, reduces silent faults that the owner has no way of detecting from inside the shop.
