I have an Olympus VN-4100PC. It will record something like 20 hours of audio. Said audio can be downloaded to a PC via USB. Since it records such a large amount of audio, it's feasible to leave it on continuously, deleting the recording every few hours (presuming nothing of interest has happened). This way, you don't have to think about turning it on, just have to replace the batteries (2 AAA) every day or so.
Take a look at your cell phone. See if the cell phone has a recording capability. Some cell phones have a significant amount of on-board memory and can easily record hours of audio. Said audio can likely be copied to a PC.
You might also see if it's possible to use your cell phone to leave a message to your own voice mail. The key thing would be how long a voice message you could leave. The advantage of sending yourself a voice mail is that the recording is then external to you. A recorder or cell phone can disappear or get lost in the evidence room, or can be mysteriously erased. A voice mail you send yourself can't. If your cell phone allows you to do this, program a speed dial key on the cell phone so all you have to do is hold that key down for a couple of seconds to start recording.
If a situation is developing that looks like it could go bad, whether it involves police or not, calling 911 isn't a bad idea. 911 calls are recorded and those recordings can be used in court. If police are involved in an incident and beginning to get out of line, a dispatcher might be able to involve higher ranking supervisors pretty quickly. In any case, a 911 recording of what's going down could be useful and isn't going to get lost in an evidence room as easily as your pocket recorder might.