What does the SMS command and APN builder do?
Most GPS trackers are set up by text message. You send the device a short command with the APN, the server address, the report interval and the time zone. One wrong character, a missing space or a message that grows past one SMS is enough to leave the unit offline. This builder fills a command pattern with your values, checks every value, counts the SMS length and shows the text to copy. Nothing is sent from the page.
The Setup sheet tab gives the messages of a first setup in order. The One command tab builds a single command, such as a new interval, and lets you type the pattern printed in your manual. The Modem AT lines tab writes the AT commands that set the same APN directly on a cellular module.
Why the text has to be exact
- The APN decides whether the SIM gets data. A tracker with a wrong APN still receives texts, but it cannot open a data session, so it never shows on the platform.
- The separators are part of the command. In a space-separated command a space inside a password splits it in two. In a comma format a comma does the same.
- The SMS alphabet is small. One character outside it, such as an Arabic letter, cuts the limit from 160 to 70 characters.
Inputs you need
- The format of your device. It is printed in the manual: space-separated with a login and password, or comma-separated ending with #.
- The APN and, if the SIM contract gives them, the APN login and password.
- The server address, port and protocol of the platform that will receive the reports.
- The intervals and the time zone you want on the unit.
- The device login and password, if your unit asks for them.
How the messages are built
Each command has a pattern, for example the login, the password, the word apn and the APN value. The builder replaces every placeholder with your value. It checks the value first: an APN may use letters, digits, hyphen and dot, a port is 1 to 65535, a time zone is between -12 and 14. It also refuses a value that contains the separator of the chosen format. Empty optional values leave no extra spaces behind.
| Item | Limit |
|---|---|
| One SMS, GSM 7-bit | 160characters |
| Each part of a joined SMS, GSM 7-bit | 153characters |
| One SMS with any other character (UCS-2) | 70characters |
| Each part of a joined SMS, UCS-2 | 67characters |
| APN length | 100characters at most |
| Server port | 1 to 65,535 |
The GSM alphabet, the characters that count twice and the 70-character UCS-2 limit are in 3GPP TS 23.038. The 140-octet message, which holds 160 GSM 7-bit characters, is in 3GPP TS 23.040. Both read in version 19.0.0 on 3 November 2026. The 153 and 67 characters per joined part, the 100-character APN limit of TS 23.003 and the AT commands of TS 27.007 are still to verify against the official text. The command patterns are typical formats. Replace them with the pattern in your device manual.
The modem lines use the 3GPP commands AT+CGDCONT to define the APN and AT+CGAUTH to set PAP or CHAP login. Some modules use their own command for the same job, so check the AT manual of your module.
Worked example
A device takes the space-separated format. Login u1, password p1 and APN net.example, with no APN login, give the message u1 p1 apn net.example. That is 21 characters, all in the GSM alphabet, so it is one SMS with 139 characters to spare. In the comma format the same APN is APN,net.example#, which is 16 characters.
Now put a backtick in the device password. The backtick is not in the GSM alphabet, so the whole message becomes UCS-2 and the limit is 70 instead of 160. The builder shows the change before you send. For the modem, the same APN with PAP login bob and password x1 becomes AT+CGDCONT=1,"IP","net.example" followed by AT+CGAUTH=1,1,"bob","x1".
Reading your results
- Ready. The values are accepted and the message fits one SMS in the GSM 7-bit alphabet.
- More than one SMS. The message is longer than the limit. Shorten a value or confirm that the device reads joined messages.
- Non-GSM character. A character forces UCS-2. Replace it if the device manual allows.
- Fix. A value is not accepted. The red note names the field and the rule.
Common mistakes
- Using the APN of another SIM. Public and M2M plans of the same operator can use different APNs.
- Losing the leading spaces. With no login and password a space-separated command starts with two spaces. Some apps trim them.
- Copying through a chat app. Some apps replace straight quotation marks with curly ones, which breaks the AT lines.
- Sending the next command too soon. Wait for the reply before you send the next message.
- Changing several settings at once. When the status differs, correct one setting at a time.
Assumptions and limits
The command patterns here are typical formats, not the command list of a Tracom device, and they are editable data in the page configuration. This builder cannot know the firmware on your unit or what a command does on it, so check every command against your device manual. It builds no command that cuts the engine, releases a relay or resets a unit to factory settings. APNs depend on your SIM contract, so operator APNs are not listed. The length counts the text only. Tracom does not send any message: you copy the text and send it from your own phone or platform.