March 5, 2026, 7:23 am | Read time: 5 minutes

Those who monitor their partner’s smartphone often use existing services. For example, the phone’s location features and messaging services such as WhatsApp can be checked. This allows, among other things, tracking a person’s whereabouts. Messages can also be secretly read. Those affected are often unaware of the forms of surveillance possible via smartphones.

Not Only Walls Have Ears

There are now numerous apps that enable smartphone surveillance. In many cases, these spy apps are primarily aimed at jealous individuals. The apps promise relatively comprehensive monitoring of smartphone activity. For example, the apps can locate the smartphone and make WhatsApp messages or calls—including video calls—visible and audible. Social media activity can also be tracked with some apps. Some spy apps even go so far as to enable the secret activation of the microphone without the smartphone user noticing. Taking screenshots and accessing the photo gallery of the infiltrated smartphone are also part of the features.

In the app reviews, there are many fans of surveillance. Not only are jealous partners and parents enthusiastic, but bosses also claim to “check” their employees this way. However, such applications also open the door to stalkers. Data leaked from a Thai spy app in 2022 shows that about 80 percent of buyers in Germany are men. The victims rarely find out that they are being massively monitored.

Threat of Imprisonment Like for Bodily Harm

Buyers of such an app who want to monitor someone else’s smartphone must install the spy app on the target device. The providers promise complete invisibility, so the affected person is unaware of the surveillance. Users of the app secretly learn almost everything happening on the device: who the person is calling, entire call recordings, and chat histories of all messaging services.

What most people are aware of but ignore for the sake of surveillance: Such apps are illegal without the smartphone owner’s consent. (There is only an exception for parents.) In Germany, people can face up to three years in prison—the maximum penalty for negligent bodily harm. The technology magazine “c’t” conducted a random inquiry with the state criminal police offices of Lower Saxony and Berlin. The result is sobering. In the years examined, there were hardly any criminal proceedings or investigations due to the criminal use of such apps. The dark figure is very high, however. Since the market offers various apps, the number of users is likely much larger.

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How to Track Down Spy Apps

Although surveillance apps are difficult to detect on the smartphone because they are usually invisible, there are some indicators that can reveal them.

Signs of a spy app on the smartphone include:

• Increased battery consumption: The app’s processes lead to faster battery drain.
• Increased data usage: Sending files in the background to the spy app user causes higher data consumption.
• Complications on the smartphone: Both the app’s processes and software errors can slow down the smartphone and lead to strange messages.

If you suspect a spy app is on your smartphone, you can take the following measures:

• Immediate short-term solution: Activate airplane mode and disconnect Wi-Fi to stop data transmission
• Disable unknown device administrators
• Check web access from messengers. Look under “logged-in devices” to see which devices have access and block them if necessary
• Reset the device to factory settings if necessary
• Change passwords

Spy Defense on Android and iOS

Google’s Play Protect offers Android users a security feature that scans all apps on the device. Play Protect can be found in the Google Play Store. Go to your profile and then to the “Manage apps and device” tab. In the overview, there is an entry from Play Protect, which reads: “No harmful apps found” on a clean smartphone. You can also manually prompt Play Protect to scan.

Additionally, Android now warns about apps that disguise themselves or demand particularly extensive access rights and informs users when an application accesses sensitive data for an extended period. Security gaps are also closed through regular updates, which should be installed as soon as possible.

A generally recommended privacy setting is the restrictive granting of permissions. Many apps request more permissions during installation than are really necessary for proper use. Those who send voice messages via WhatsApp will likely need to enable their microphone, but can still deny access to their location. In the settings, you can call up all apps under “Apps” on Android and view the specific permissions granted. If you discover a suspicious app, you can revoke its permissions or delete the app entirely. Since newer Android versions, permissions can also be restricted to “Only while using the app” or automatically revoked if an app has not been used for a long time.

In general, prevention is better than a cure. Protect your smartphone with a password and do not let it fall into the wrong hands. Apple has also expanded its protection mechanisms in recent years. iPhones, for example, indicate with colored dots when the camera or microphone is active and document in the App Privacy Report which applications access sensitive data. For particularly vulnerable individuals, there is also an optional extreme protection called “Lockdown Mode,” which significantly restricts potential entry points for advanced spyware. If parents want to track their children’s location, it is also a matter of respect not to secretly invade the child’s privacy.