# AlgoPIN Codes
AlgoPIN generates valid PIN codes for a lock without WiFi, cellular, or remote access to the lock.
## How It Works
```mermaid
sequenceDiagram
Note over Your Server, Our Server: igloohome API
Your Server->>Our Server: Request AlgoPIN
Our Server-->>Your Server: AlgoPIN code
Your Server->>Guest: AlgoPIN code
Guest->>Lock: Enter AlgoPIN code
Lock->>Lock: Unlock
```
## Types of AlgoPIN Codes
| Type | Validity | Variances | API |
| --- | --- | --- | --- |
| One-Time (OTP) | Single use | 10 | [Create a One-Time AlgoPIN](/home/api_access#create-a-one-time-algopin) |
| Permanent | No end date | 10 | [Create a Permanent AlgoPIN](/home/api_access#create-a-permanent-algopin) |
| Duration (Hourly) | 1 to 672 hours | 3 | [Create an Hourly AlgoPIN](/home/api_access#create-an-hourly-algopin) |
| Duration (Daily) | 29 to 367 days | 3 | [Create a Daily AlgoPIN](/home/api_access#create-a-daily-algopin) |
| Passage | 1 to 12 hours | 1 | [Create a Passage AlgoPIN](/home/api_access#create-a-passage-algopin) |
A Passage AlgoPIN unlocks the lock and keeps it unlocked for the chosen number of hours. Passage requires newer lock firmware.
## Activation
AlgoPIN codes valid for more than 24 hours need activation on the lock. The first time the code is used on the lock, it is activated. That first use must happen within the 24-hour activation window, which starts when the code's validity starts.
The example below uses a code valid from 00:00, 1 Oct to 00:00, 5 Oct. The activation window is the first 24 hours of validity, from 00:00, 1 Oct to 00:00, 2 Oct. The timelines are not drawn to scale.
**First use within the activation window.** The code is activated, unlocks the lock, and stays valid until 00:00, 5 Oct.
**First use after the activation window.** The code was not activated in the window. The lock does not unlock, even though the code is still within its validity period.
## AlgoPIN Limitations
| Limitation | Explanation |
| --- | --- |
| AlgoPIN-supported devices only | The device has to support AlgoPIN. See [Supported Devices](/home/supported-devices). |
| Paired devices | Pair the device with the igloohome app first. |
| 24-hour activation | AlgoPIN codes valid for more than 24 hours need activation on the lock. The first use must be within the first 24 hours of validity. See [Activation](#activation). |
| 256 rule | You can't delete an AlgoPIN whose start date is more than 256 hours after its creation. |
| 199 rule | The lock's whitelist and blacklist hold at most 199 PIN codes in total (AlgoPIN and Bluetooth PIN codes). |
| PINs per duration | For one duration, you can generate only as many PINs as the type's [variances](#variance-multiple-algopin-codes-for-the-same-duration). |
## Variance: Multiple AlgoPIN Codes for the Same Duration
For a given duration, each variance returns a different PIN code. The Types table above lists the number of variances per type.
One-Time and Permanent support 10 variances on locks with newer firmware. Some older locks gain this with a firmware update; others support 5.
Example of hourly PIN codes for one lock, three variances each:
| Start time | End time | PIN codes (variance 1, 2, 3) | deviceId |
| --- | --- | --- | --- |
| 2PM | 3PM | 511093918, 945844647, 052368115 | IGB403fe3b9d |
| 2PM | 4PM | 633654730, 437755350, 337288611 | IGB403fe3b9d |
| 3PM | 5PM | 297248165, 196981787, 384522901 | IGB403fe3b9d |
| 3PM | 5PM | 948950871, 142404925, 817840781 | IGP114cde456 |
The following request returns a unique PIN code (e.g. `4642226`):
```bash
curl --request POST \
--url https://api.igloohome.co/home/devices/IGP101abc123/algopin/onetime \
--header 'Content-Type: application/json' \
--header 'Authorization: Bearer abcdef' \
--data '{
"variance": 1,
"startDate": "2022-01-01T00:00:00+08:00",
"accessName": "Maintenance guy"
}'
```
Changing the variance returns a second unique PIN code (e.g. `1419472`) for the same duration:
```bash
curl --request POST \
--url https://api.igloohome.co/home/devices/IGP101abc123/algopin/onetime \
--header 'Content-Type: application/json' \
--header 'Authorization: Bearer abcdef' \
--data '{
"variance": 2,
"startDate": "2022-01-01T00:00:00+08:00",
"accessName": "Maintenance guy 2"
}'
```