> For the complete documentation index, see [llms.txt](https://docs.idlayr.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.idlayr.com/api-reference/sim-check/introduction.md).

# Introduction

The IDlayr SIM Swap API reports whether the SIM card associated with a phone number has been changed recently. It does so without sending an SMS or any visible challenge, and without any device participation: the platform queries the mobile network operator (MNO) directly for the SIM-change timestamp and resolves the Check server-side.

The Check resolves in a single request:

1. **Create** the Check with the phone number you want to verify and (optionally) a `period` to scope the change-detection window. The response already contains the terminal `status` (`COMPLETED` or `ERROR`) along with the result fields below.
2. **Retrieve** a Check at any time with `GET /v1/sim-swap-checks/{check_id}`, for example to reconcile against your own records.

When `status` is `COMPLETED`, the response includes:

* `no_sim_change` — whether the SIM card has *not* been changed within `no_sim_change_period`.
* `sim_change_within` — the time bucket containing the most recent SIM change (when known).
* `network_id` — the network operator that resolved the request.

Requests authenticate with an OAuth2 Access Token in the `Authorization` header (`Bearer {access_token}`). Tokens are created using a project's `client_id` and `client_secret`.


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