| Number | Name | Date | Kind |
|---|---|---|---|
| 4304971 | Flax | Dec 1981 | |
| 4323739 | Flax et al. | Apr 1982 |
| Number | Date | Country |
|---|---|---|
| 2812540 | Sep 1979 | DEX |
| 2916630 | Nov 1980 | DEX |
| 2919599 | Nov 1980 | DEX |
| 2922662 | Jan 1981 | DEX |
| 3013944 | Oct 1981 | DEX |
| 3205626 | Aug 1983 | DEX |
| Entry |
|---|
| Telephony, "Phone Lock Product", Jun. 1, 1981, p. 118. |