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| Company name | Primary business area | Primary coverage | |
|---|---|---|---|
| On-Net Surveillance Systems, Inc. | Software | Global | |
| Oncam Grandeye | CCTV | Global | |
| O & M Software Ltd | Software | ||
| O' Rourke Security Systems | Intruder alarm | Ireland | |
| O'Connor's Singapore Pte Ltd | Integrated security | Singapore | |
| O-SECUL Nigeria Limited | Integrated security | Nigeria | |
| Oakpark Alarms | CCTV | United Kingdom (UK) | |
| Oakpark Alarms Security Services Ltd | CCTV | United Kingdom (UK) | |
| Oakwood Automation Systems | CCTV | United States of America (USA) | |
| OAS (UK) Ltd | CCTV | United Kingdom (UK) | |
| Oasis Enterprises L.L.C. | Digital video recording | United Arab Emirates | |
| OB Telecom Electronics Co. Ltd. | Transmission systems | Global | |
| Oberthur Technologies | Cards and readers | United States of America (USA) | |
| Oberthur Technologies S.A. | Access control | France | |
| ObjectVideo | Software | United States of America (USA) | |
| Observation Technologies, Inc. | Central monitoring systems | United States of America (USA) | |
| Observint Technologies | Access control | United States of America (USA) | |
| Océ (Schweiz) AG | CCTV | France | |
| Ocean Presence Technologies | Underwater video | Global | |
| OCS Group | Integrated security | United Kingdom (UK) | |
| OCS Resolution Ltd | Manned guarding | United Kingdom (UK) | |
| OCS Security Services | CCTV | United Kingdom (UK) | |
| Octagon Ltd | CCTV | United Kingdom (UK) | |
| Octalys | IP networking products | Morocco | |
| Octavian Security | Manned guarding | United Kingdom (UK) | |
| Octavian Security (USA) Inc. | Manned guarding | United States of America (USA) | |
| OD Security | CCTV | Netherlands | |
| Odak Guvenlik Sistemleri Ltd. Sti. | Digital video recording | Turkey | |
| Odesys Solutions Ltd. | CCTV | United Kingdom (UK) | |
| ODI Security | Access control | United States of America (USA) | |


