VivoKey Thermo for iOS

VivoKey Thermo is a free iOS app that reads your body temperature straight from a VivoKey Thermo NFC implant with a tap of your phone, and keeps a simple history so you can see how it changes over time. It's an independent project by Petr Ziegner, not affiliated with or endorsed by VivoKey.

Coming Soon on the App Store

Overview Privacy Policy Support Donate

Screenshots

Capabilities

Read in Seconds

Hold your phone near the implant and get a reading right away, no waiting around and nothing to set up first.

Your History, Saved

Every reading you take stays right on your phone, so you can look back and see how things have changed whenever you want.

Watch the Trend

A simple graph turns your readings into a line you can actually read, so patterns over days or weeks jump out at a glance.

Tuned to You

Adjust a personal calibration so the number on screen matches what feels right for your body.

How the Reading Works

The implant has no battery. It borrows a little power from your phone's NFC signal just long enough to take one measurement, so getting a reading is a quick back-and-forth:

Wake it up Your phone's NFC beams over just enough power to switch the implant on.

Reach the sensor The app talks to the tiny temperature sensor tucked inside the implant.

Take the measurement The sensor takes a fresh reading, and the app waits a moment for it to finish.

Turn it into a temperature The raw signal gets converted into an actual number, in Celsius.

Save it for later The reading is added to your history, with your personal calibration applied when it's shown to you.

For anyone curious about the hardware side, here's exactly what happens under the hood.

Chip	NXP NTAG5Link-class (ISO15693-3), with an on-board I2C bridge to a TMP112 sensor by default. TMP117 and TMP119 are also supported and auto-detected.
Chip commands	`0xC0` READ_CONFIG, `0xC1` WRITE_CONFIG, `0xD2` READ_SRAM, `0xD4` WRITE_I2C, `0xD5` READ_I2C.
Energy harvesting	Writing the EH_CONFIG register (`0xA7`) triggers it. The app polls for the LOAD_OK bit, then enables output.
iOS command framing	Only `NFCISO15693Tag.customCommand` with `requestFlags: [.highDataRate]` (non-addressed) works on real hardware.
Manufacturer code quirk	Never prepend the NXP code `0x04` manually. CoreNFC adds it automatically. Adding it yourself causes a "Tag connection lost" error.
Address flag quirk	Setting the `.address` flag causes an "Invalid Parameter" error instead.
Response framing	CoreNFC strips the ISO15693 response flag byte, so command responses come back data-only.
TMP112 math	`(rawInt16 >> 4) * 0.0625`
TMP117 / TMP119 math	`rawInt16 * 0.0078125`
Conversion ready	Signalled by bit 15 (the OS bit) in the sensor's config register.

Last updated: 2026-07-27

The App

VivoKey Thermo is developed and maintained independently by Petr Ziegner. The application reads a temperature value over NFC from a compatible implant and displays it, together with a locally stored history of prior readings. The app operates entirely on your device, except for the optional download of the public Hall of Fame donor list described below.

Data We Collect

VivoKey Thermo does not collect, transmit, or store personal information on any server. Specifically:

Your temperature reading history is stored exclusively on your device.
The application does not transmit this history to us, or to any third party.
No name, email address, device identifier, or location data is ever requested or stored.

Body temperature readings are health-related information, so to be explicit: these readings stay exclusively on your device. The application does not upload them, does not transmit them, and does not process them on any server operated by the developer, and it does not share them with third parties.

Network Activity

The only network request intentionally initiated by the application is an HTTP GET to petrziegner.cz/vkthermo/halloffame, which fetches a public JSON file listing donors for display in the app. It's unauthenticated and isn't tied to any account or user identifier, and it never includes your temperature history or any other data from the app. Like any HTTPS request, it naturally reveals standard network-level details, such as your IP address, to the network it travels through, but nothing beyond that is sent.

Device Permissions

VivoKey Thermo uses Apple's Core NFC framework to communicate with compatible VivoKey Thermo implants over Near Field Communication (NFC). This communication is used only to obtain the current temperature reading; it is not logged or retained beyond the reading saved to your on-device history. The application does not request access to your location, contacts, camera, microphone, photo library, calendar, or any other sensitive device information.

Third-Party Services

VivoKey Thermo does not include any third-party SDKs for analytics, advertising, crash reporting, profiling, or tracking.

Accounts & Data Sale

There is no account system, login mechanism, or server-side user profile. As no personal data is collected, there is none to sell, and none to share with advertisers or data brokers.

GDPR & Data Rights

Because VivoKey Thermo does not process personal data on servers on your behalf, certain rights that apply to server-held personal information, such as requests for access, correction, or deletion, generally do not apply here, since no server-side record exists to access, correct, or delete. Your on-device temperature history remains fully within your control at all times; see "Deleting Your Data" below.

Children's Privacy

VivoKey Thermo does not collect personal information from any user, regardless of age. Because no personal data is collected or processed, there is nothing additional to consider here specifically for children.

Deleting Your Data

Because your reading history is stored exclusively on your device, you retain full control over it at all times:

Individual readings may be deleted, or your full history cleared, from within the application; or
The application may be deleted entirely, which removes all locally stored data along with it.

Changes to This Policy

Should this policy change, the revision will be posted on this page along with an updated "last updated" date.

Contact

Questions regarding privacy or this policy may be directed as follows:

Contact form

Not affiliated with VivoKey. VivoKey Thermo is an independent, third-party application. It is not affiliated with, endorsed by, or sponsored by VivoKey Technologies or any of its partners. The term "VivoKey" is used solely to describe compatibility with the implant hardware.

Troubleshooting

Reposition your phone along the implant. The NFC antenna is usually near the top-back of the phone, not the center. Remove any phone case, especially thick or magnetic ones, which can block the signal. Then hold the phone steady against the implant for a few seconds without moving it.

Accuracy depends on implant depth and placement, and can vary from person to person. VivoKey Thermo readings are for general personal tracking only and should not be treated as a clinical or medical-grade measurement.

Other Ways to Help

Not everyone can donate, and that's completely fine. There are other ways to support the project:

Tinker with the reading timings in advanced settings and let me know what works best for you.
Suggest a feature you'd like to see.
Report bugs you run into.

Direct Contact

Prefer to reach out directly instead of the form below? Use either of these:

Contact Form

Fill in whatever you're comfortable sharing. Name and email are optional. If you leave an email, I'll reply there.

Name (optional)

Email (optional)

Type

Message

No account needed. Your message is sent directly to Petr, no third parties involved.